CHAPTER XIV

MAMMALS (BEASTS AND MAN)

SUGGESTIONS.--A tame rabbit, a house cat, or a pet squirrel may be taken to the school and observed by the class. Domestic animals may be observed at home and on the street. A study of the teeth will give a key to the life of the animal, and the teacher should collect a few mammalian skulls as opportunities offer. The pupils should be required to identify them by means of the chart of skulls (p. 194). If some enthusiastic students fond of anatomy should dissect small mammals, the specimens should be killed with chloroform, and the directions for dissection usual in laboratory works on this subject may be followed. There is a brief guide on page 223. The following outline for the study of a live mammal will apply almost as well to the rabbit or squirrel as to the cat.

=The Cat.=--The house cat (_Felis domestica_) is probably descended from the Nubian cat (_Felis maniculata_, Fig. 333) found in Africa. The wild species is about half again as large as the domestic cat, grayish brown with darker stripes; the tail has dark rings. The lynx, or wild cat of America (_Lynx rufus_), is quite different. Compare the figures (333, 335) and state three obvious differences. To which American species is the house cat closer akin, the lynx (Fig. 335) or the ocelot (Fig. 334)? The domestic cat is found among all nations of the world. What is concluded, as to its nearest relatives, from the fact that the Indians had no cats when America was discovered? It was considered sacred by the ancient Egyptians, and after death its body was embalmed.

The =body of the cat= is very flexible. It may be divided into five regions, the head, neck, trunk, tail, and limbs. Its eyes have the same parts as the eyes of other mammals. Which part of its eye is most peculiar? (Fig. 333.) What part is lacking that is present in birds? How are the eyes especially adapted for seeing at night? Does the pupil in the light extend up or down or across the iris? Does it ever become round?

[Illustration: FIG. 333.--WILD CAT OF AFRICA (_Felis maniculata_), × ¹⁄₈.]

What is the shape and position of the _ears_? Are they large or small compared with those of most mammals? They are fitted best for catching sound from what direction? What is thus indicated in regard to the cat’s habits? (Compare with ears of rabbit.) Touch the _whiskers_ of the cat. What result? Was it voluntary or involuntary motion? Are the _nostrils_ relatively large or small compared with those of a cow? Of man?

Is the _neck_ long or short? Animals that have long fore legs usually have what kind of a neck? Those with short legs? Why? How many _toes_ on a fore foot? Hind foot? Why is this arrangement better than the reverse? Some mammals are sole walkers (_plantigrade_), some are toe walkers (_digitigrade_). To which kind does the cat belong? Does it walk on the ends of the toes? Does it walk with all the joints of the toes on the ground? Where is the _heel_ of the cat? (Fig. 334.) The _wrist_? To make sure of the location of the wrist, begin above: find the shoulder blade, the upper arm (one or two bones?), the lower arm (one or two bones?), the wrist, the palm, and the fingers (Fig. 337). Is the heel bone prominent or small?

[Illustration: FIG. 334.--OCELOT (_Felis pardalis_), of Texas and Mexico, × ¹⁄₉.]

In what direction does the _knee_ of the cat point? The heel? The elbow? The wrist? Compare the front and hind _leg_ in length; straightness; heaviness; number and position of toes; sharpness of the _claws_. What makes the _dog’s claws_ duller than a cat’s? What differences in habit go with this? Judging from the toe that has become useless on the fore foot of the cat, which toe is lacking in the hind foot? Is it the cat’s thumb or little finger that does not touch the ground? (Fig. 337.) Locate on your own hand the parts corresponding to the pads on the forefoot of a cat. Of what use are soft pads on a cat’s foot?

Some animals have short, soft =fur= and long, coarse over hair. Does the cat have both? Is the cat’s fur soft or coarse? Does the fur have a color near the skin different from that at the tip? Why is hair better suited as a covering for the cat than feathers would be? Scales? Where are long, stiff bristles found on the cat? Their length suggests that they would be of what use to a cat in going through narrow places? Why is it necessary for a cat to be noiseless in its movements?

[Illustration: FIG. 335.--LYNX (_Lynx rufus_). The “Bob-tailed cat” (North America).]

Observe the =movements of the cat=.--Why cannot a cat come down a tall tree head foremost? Did you ever see a cat catch a bird? How does a cat approach its prey? Name a jumping insect that has long hind legs; an amphibian; several mammals (Figs. 362, 374). Does a cat ever trot? Gallop? Does a cat chase its prey? When does the cat move with its heel on the ground? The claws of a cat are withdrawn by means of a tendon (see Fig. 338). Does a cat seize its prey with its mouth or its feet?

How does a cat make the purring sound? (Do the lips move? The sides?) How does a cat drink? Do a cat and dog drink exactly the same way? Is the cat’s tongue rough or smooth? How is the tongue used in getting the flesh off close to the bone? Can a cat clean a bone entirely of meat?

[Illustration: FIG. 336.--JAGUAR, of tropical America.]

In what state of development is a newly born kitten? With what does the cat _nourish its young_? Name ten animals of various kinds whose young are similarly nourished. What is this class of animals called? Why does a cat bend its back when it is frightened or angry? Does _a cat or a dog_ eat a greater variety of food? Which refuses to eat an animal found dead? Will either bury food for future use? Which is sometimes troublesome by digging holes in the garden? Explain this instinct. Which lived a solitary life when wild? Which had a definite haunt, or home? Why are dogs more sociable than cats? A dog is more devoted to his master. Why? A cat is more devoted to its home, and will return if carried away. Why? Why does a dog turn around before lying down? (Consider its original environment.)

[Illustration: FIG. 337.--SKELETON OF CAT.]

=The Skeleton= (Fig. 337).--Compare the _spinal column_ of a cat in form and flexibility with the spinal column of a fish, a snake, and a bird.

The _skull_ is joined to the spinal column by two knobs (or _condyls_), which fit into sockets in the first vertebra. Compare the jaws with those of a bird and a reptile. There is a prominent ridge in the temple to which the powerful chewing muscles are attached. There is also a ridge at the back of the head where the muscles which support the head are attached (Fig. 348).

[Illustration: FIG. 338.--CLAW OF CAT (1) retracted by ligament, and (2) drawn down by muscle attached to lower tendon.]

Count the _ribs_. Are there more or fewer than in man? The breastbone is in a number of parts, joined, like the vertebræ, by cartilages. Compare it with a bird’s sternum; why the difference? The shoulder girdle, by which the front legs are attached to the trunk, is hardly to be called a girdle, as the collar bones (clavicles) are rudimentary. (They often escape notice during dissection, being hidden by muscles.) The shoulder blades, the other bones of this girdle, are large, but relatively not so broad toward the dorsal edge as human shoulder blades. The clavicles are tiny because they are useless. Why does the cat not need as movable a shoulder as a man? The pelvic, or hip girdle, to which the hind legs are attached, is a rigid girdle, completed above by the spinal column, to which it is immovably joined. Thus the powerful hind legs are joined to the most rigid portion of the trunk.

=Mammals.=--The cat belongs to the _class Mammalia_ or mammals. The characteristics of the class are that the young are not hatched from eggs, but _are born alive, and nourished with milk_ (hence have lips), and the _skin is covered with hair_. The milk glands are situated ventrally. The position of the class in the animal kingdom was shown when the cow was classified (p. 9). Their care for the young, their intelligence, and their ability to survive when in competition with other animals, causes the mammals to be considered the highest class in the animal kingdom.

According to these tests, what class of vertebrates should _rank next to mammals_? Compare the heart, lungs, blood, and parental devotion of these two highest classes of animals.

[Illustration: FIG. 339.--SKELETON OF LION (cat family).]

=The first mammals=, which were somewhat like small opossums, appeared millions of years ago, when the world was inhabited by giant reptiles. These reptiles occupied the water, the land, and the air, and their great strength and ferocity would have prevented the mammals from multiplying (for at first they were small and weak), but the mammals carried their young in a pouch until able to care for themselves, while the reptiles laid eggs and left them uncared for. The first mammals used reptilian eggs for food, though they could not contend with the great reptiles. Because birds and mammals are better parents than reptiles, they have conquered the earth, and the reptiles have been forced into subordination, and have become smaller and timid.

[Illustration: FIG. 340.--WALRUS (_Trichechus rosmarus_).]

=Classification of Mammals.=--Which two have the closest _resemblances_ in the following lists: Horse, cow, deer. Why? Cat, cow, bear. Why? Monkey, man, sheep. Why? Rat, monkey, squirrel. Why? Giraffe, leopard, camel. Why? Walrus, cat, cow. Why? Check the five mammals in the following lists that form a group _resembling each other most closely_: Lion, bear, pig, dog, squirrel, cat, camel, tiger, man. State your reasons. Giraffe, leopard, deer, cow, rat, camel, hyena, horse, monkey. State reasons.

[Illustration: FIG. 341.--WEASEL, in summer; in Canada in winter it is all white but tip of tail.]

=Teeth and toes= are the basis for subdividing the class mammalia into orders. Although the breathing, circulation, and internal organs and processes are similar in all mammals, the external organs vary greatly because of the varying environments of different species. The internal structure enables us to place animals together which are essentially alike; _e.g._ the whale and man are both mammals, since they resemble in breathing, circulation, and multiplication of young. The external organs guide us in separating the class into orders. The teeth vary according to the food eaten. The feet vary according to use in obtaining food or escaping from enemies. This will explain the difference in the length of legs of lion and horse, and of the forms of the teeth in cat and cow. Make a careful study of the teeth and limbs as shown in the figures and in all specimens accessible. Write out the dental formulas as indicated at the top of page 194. The numerals above the line show the number of upper teeth; those below the line show the number of lower teeth in one half of the jaw. They are designated as follows: _I_, incisors; _C_, canine; _M_, molars. Multiplying by two gives the total number. Which skulls in the chart have the largest canines? Why? The smallest, or none at all? Why? Compare the molars of the cow, the hog, and the dog. Explain their differences. In which skulls are some of the molars lacking? Rudimentary? Why are the teeth that do not touch usually much smaller than those that do?

[Illustration: FIG. 342.--FOOT OF BEAR (_Plantigrade_).]

[Illustration: FIG. 343.--POLAR BEAR (_Ursus maritimus_).]

KEY, OR TABLE, FOR CLASSIFYING MAMMALS (_class Mammalia_) INTO ORDERS

Orders

A₁ =Imperfect Mammals=, young hatched or prematurely born

B₁ Jaws a birdlike beak, egg-laying _Mon′otremes_

B₂ Jaws not beaklike, young carried in pouch _Marsu′pials_

A₂ =Perfect Mammals=, young not hatched, nor prematurely born

{C₁ Front part of both jaws lack { teeth _Eden′tates_ { B₁ {C₂ Teeth with sharp points for _Digits { piercing shells of insects _Insect′ivors_ with { claws_ {C₃ Canines very long, molars suited { for tearing _Car′nivors_ { {C₄ Canines lacking, incisors very { large _Rodents_

B₂ {C₁ Head large; carnivorous _Ceta′ceans_ _Digits { not {C₂ Head small; herbivorous _Sire′neans_ distinct_{

{C₁ Five toes, nose prolonged into a { snout _Proboscid′eans_ { {C₂ Toes odd number, less than five _E′quines_ } B₃ { } _Digits {C₃ Toes even number, upper front }_Un- with { teeth lacking, chew the cud _Ru′minants_ } gu- nails or{ }lates_ hoofs_ {C₄ Toes even number, upper front } { teeth present, not cud-chewers _Swine_ } { {C₅ All limbs having hands _Quad′rumans_ { {C₆ Two limbs having hands _Bi′mans_

=Exercise in Classification.=--Copy the following list, and by reference to figures write the name of its order after each mammal:--

Ape (Figs. 405, 406) Rabbit (Fig. 345) Dog (Figs. 356, 408) Hog (Figs. 357, 393) Bat (Figs. 347, 370) Cat (Figs. 337, 348) Armadillo (Figs. 349, 365) Cow (Figs. 344, 386) Walrus (Fig. 340) Monkey (Figs. 352, 401) Horse (Figs. 355, 395) Ant-eater (Figs. 354, 364) Antelope (Fig. 391) Mole (Figs. 367, 368) Beaver (Figs. 372, 373) Duckbill (Fig. 359) Tapir (Fig. 384) Dolphin (Figs. 379, 397)

Use chart of skulls and Figs. 381, 382, 395-400 in working out this exercise.

=Chart of Mammalian Skulls (Illustrated Study)=

5 1 2 Man’s dental formula is (_M_ -, _C_ -, _I_ -)² = 32. 5 1 2

In like manner fill out formulas below:--

Cow (_M_ - _C_ - _I_ -)² = 32 Rabbit (_M_ - _C_ - _I_ -)² = 28 Walrus (_M_ - _C_ - _I_ -)² = 34 Bat (_M_ - _C_ - _I_ -)² = 34 Cat (_M_ - _C_ - _I_ -)² = 30 Armadillo (_M_ - _C_ - _I_ -)² = 28 Horse (_M_ - _C_ - _I_ -)² = 40 Whale (_M_ - _C_ - _I_ -)² = 0 Am. Monkey (_M_ - _C_ - _I_ -)² = 36 Sloth (_M_ - _C_ - _I_ -)² = 18 Ant-eater (_M_ - _C_ - _I_ -)² = 0 Dog (_M_ - _C_ - _I_ -)² = 42 Hog (_M_ - _C_ - _I_ -)² = 44 Sheep (_M_ - _C_ - _I_ -)² = 32

[Illustration: FIG. 344.--Skull and front of lower jaw of COW.]

[Illustration: FIG. 345.--RABBIT.

_A_, _B_, incisors; _C_, molars.]

[Illustration: FIG. 346.--WALRUS (see Fig. 341).]

[Illustration: FIG. 347.--BAT.]

[Illustration: FIG. 348.--CAT.]

=Chart of Mammalian Skulls=

[Illustration: FIG. 349.--ARMADILLO.]

[Illustration: FIG. 350.--HORSE (front of jaw).]

[Illustration: FIG. 351.--GREENLAND WHALE.]

[Illustration: FIG. 352.--AMERICAN MONKEY.]

[Illustration: FIG. 353.--SLOTH (Fig. 363).]

[Illustration: FIG. 354.--ANT-EATER (Fig. 364).]

[Illustration: FIG. 355.--HORSE.]

[Illustration: FIG. 356.--DOG. Upper (_A_) and lower (_B_) jaw.]

[Illustration: FIG. 357.--HOG.]

[Illustration: FIG. 358.--SHEEP.]

The =lowest order of mammals= contains only two species, the duckbill and the porcupine ant-eater, both living in the Australian region. Do you judge that the _duckbill_ of Tasmania (Fig. 359) lives chiefly in water or on land? Why? Is it probably active or slow in movement? It dabbles in mud and slime for worms and mussels, etc. How is it fitted for doing this? Which feet are markedly webbed? How far does the web extend? The web can be folded back when not in use. It lays two eggs in a nest of grass at the end of a burrow. Trace resemblances and differences between this animal and birds.

[Illustration: FIG. 359.--DUCKBILL (_Ornithorhynchus paradoxus_).]

[Illustration: FIG. 360.--SPINY ANT-EATER (_Echidna aculeata_). View of under surface to show pouch. (After Haacke.)]

The _porcupine ant-eater_ has numerous quill-like spines (Fig. 360) interspersed with its hairs. (Use?) Describe its claws. It has a long prehensile tongue. It rolls into a ball when attacked. Compare its jaws with a bird’s bill. It lays one egg, which is carried in a fold of the skin until hatched. Since it is pouched it could be classed with the pouched mammals (next order), but it is egg-laying. Suppose the two animals in this order did not nourish their young with milk after hatching, would they most resemble mammals, birds, or reptiles?

Write the name of this _order_. ____ (See Table, p. 193.) _Why_ do you place them in this order (____)? (See p. 193.) The name of the order comes from two Greek words meaning “one opening,” because the ducts from the bladder and egg glands unite with the large intestine and form a cloaca. What other classes of vertebrates are similar in this?

[Illustration: FIG. 361.--OPOSSUM (_Didelphys Virginianus_).]

=Pouched Mammals.=--These animals, like the last, are numerous in the Australian region, but are also found in South America, thus indicating that a bridge of land once connected the two regions. The _opossum_ is the only species which has penetrated to North America (Fig. 361). Are its jaws slender or short? What kinship is thus suggested? As shown by its grinning, its lips are not well developed. Does this mean a low or a well-developed mammal? Where does it have a thumb? (Fig. 361.) Does the thumb have a nail? Is the tail hairy or bare? Why? Do you think it prefers the ground or the trees? State two reasons for your answer. It hides in a cave or bank or hollow tree all day, and seeks food at night. Can it run fast on the ground? It feigns death when captured, and watches for a chance for stealthy escape.

The _kangaroo_ (Fig. 362), like the opossum, gives birth to imperfectly developed young. (Kinship with what classes is thus indicated?) After birth, the young (about three fourths of an inch long) are carried in a ventral pouch and suckled for seven or eight months. They begin to reach down and nibble grass before leaving the pouch. Compare fore legs with hind legs, front half of body with last half. Describe tail. What is it used for when kangaroo is at rest? In jumping, would it be useful for propelling and also for balancing the body? Describe hind and fore feet. _Order_ ____. _Why?_ ____. See key, page 193.

[Illustration: FIG. 362.--GIANT KANGAROO.]

=Imperfectly Toothed Mammals.=--These animals live chiefly in South America (sloth, armadillo, giant ant-eater) and Africa (pangolin). The sloth (Fig. 363) eats leaves. Its movements are remarkably slow, and a vegetable growth resembling moss often gives its hair a green color. (What advantage?) How many toes has it? How are its nails suited to its manner of living? Does it save exertion by hanging from the branches of trees instead of walking upon them?

[Illustration: FIG. 363.--SLOTH of South America.]

[Illustration: FIG. 364.--GIANT ANT-EATER of South America. (See Fig. 354.) Find evidences that the edentates are a degenerate order. Describe another ant-eater (Fig. 360).]

Judging from the figures (363, 364, 365), are the members of this order better suited for attack, active resistance, passive resistance, or concealment when contending with other animals? The ant-eater’s claws (Fig. 364) on the fore feet seem to be a hindrance in walking; for what are they useful? Why are its jaws so slender? What is probably the use of the enormous bushy tail? The nine-banded armadillo (Fig. 365) lives in Mexico and Texas. It is omnivorous. To escape its enemies, it burrows into the ground with surprising rapidity. If unable to escape when pursued, its hard, stout tail and head are turned under to protect the lower side of the body where there are no scales. The three-banded species (Fig. 366) lives in Argentina. Compare the ears and tail of the two species; give reasons for differences. Why are the eyes so small? The claws so large? _Order_ ____. _Why?_ ____.

[Illustration: FIG. 365.--NINE-BANDED ARMADILLO of Texas and Mexico. (_Dasypus novemcinctus._) It is increasing in numbers; it is very useful, as it digs up and destroys insects. (See Fig. 349.)]

[Illustration: FIG. 366.--THREE-BANDED ARMADILLO (_Tolypeutes tricinctus_).]

=Insect Eaters.=--The soft interior and crusty covering of insects makes it unnecessary for animals that prey upon them to have flat-topped teeth for grinding them to powder, or long cusps for tearing them to pieces. The teeth of insect eaters, even the molars (Fig. 368), have many sharp tubercles, or points, for holding insects and piercing the crusty outer skeleton and reducing it to bits. As most insects dig in the ground or fly in the air, we are not surprised to learn that some insect-eating mammals (the bats) fly and others (the moles) burrow. Are the members of this order friends or competitors of man?

[Illustration: FIG. 367.--THE MOLE.]

[Illustration: FIG. 368.--SKELETON OF MOLE. (Shoulder blade is turned upward.)]

Why does _the mole_ have very small eyes? Small ears? Compare the shape of the body of a mole and a rat. What difference? Why? Compare the front and the hind legs of a mole. Why are the hind legs so small and weak? Bearing in mind that the body must be arranged for digging and using narrow tunnels, study the skeleton (Fig. 368) in respect to the following: Bones of arm (length and shape), fingers, claws, shoulder bones, breastbone (why with ridge like a bird?), vertebræ (why are the first two so large?), skull (shape). There are no eye sockets, but there is a snout gristle; for the long, sensitive snout must serve in place of the small and almost useless eyes hidden deep in the fur. Is the fur sleek or rough? Why? Close or thin? It serves to keep the mole clean. The muscles of neck, breast, and shoulders are very strong. Why? The mole eats earthworms as well as insects. It injures plants by breaking and drying out their roots. Experiments show that the Western mole will eat moist grain, though it prefers insects. If a mole is caught, repeat the experiment, making a careful record of the food placed within its reach.

[Illustration: FIG. 369.--SKELETON OF BAT.]

As with the mole, the skeletal adaptations of _the bat_ are most remarkable in the hand. How many fingers? (Fig. 369.) How many nails on the hand? Use of nail when at rest? When creeping? (Fig. 369.) Instead of feathers, the flying organs are made of a pair of extended folds of the skin supported by elongated bones, which form a framework like the ribs of an umbrella or a fan. How many digits are prolonged? Does the fold of the skin extend to the hind legs? The tail? Are the finger bones or the palm bones more prolonged to form the wing skeleton?

[Illustration: FIG. 370.--VAMPIRE (_Phyllostoma spectrum_) of South America. × ¹⁄₆.]

The skin of the wing is rich in blood vessels and nerves, and serves, by its sensitiveness to the slightest current of air, to guide the bat in the thickest darkness. Would you judge that the bat has sharp sight? Acute hearing?

The moles do not _hibernate_; the bats do. Give the reason for the difference. If bats are aroused out of a trance-like condition in winter, they may die of starvation. Why? The mother bat carries the young about with her, since, unlike birds, she has no nest. How are the young nourished? _Order_ ____. _Why?_ ____. (Key, p. 193.)

[Illustration: FIG. 371.--POUCHED GOPHER (_Geomys bursarius_) × ¹⁄₄, a large, burrowing field rat, with cheek pouches for carrying grain.]

[Illustration: FIG. 372.--Hind foot _a_, fore foot _b_, tail _c_, of BEAVER.]

[Illustration: FIG. 373.--BEAVER.]

[Illustration: FIG. 374.--POSITION OF LIMBS IN RABBIT.]

=The Gnawing Mammals.=--These animals form the most numerous order of mammals. They _lack canine_ teeth. Inference? The incisors are four in number in all species except the rabbits, which have six (see Fig. 345). They are readily recognized by their _large incisors_. These teeth grow throughout life, and if they are not constantly worn away by gnawing upon hard food, they become inconveniently long, and may prevent closing of the mouth and cause starvation. The hard enamel is all on the front surface, the dentine in the rear being softer; hence the incisors sharpen themselves by use to a chisel-like edge. The molars are set close together and have their upper surfaces level with each other. The ridges on them run crosswise so as to form a continuous filelike surface for reducing the food still finer after it has been gnawed off (Fig. 345). The lower jaw fits into grooves in place of sockets. This allows the jaw to work back and forth instead of sidewise. The rabbits and some squirrels have a hare lip; _i.e._ the upper lip is split. What advantage is this in eating? In England the species that burrow are called rabbits; those that do not are called hares.

Name six enemies of rabbits. Why does a rabbit usually sit motionless unless approached very close? Do you usually see one before it dashes off? A rabbit has from three to five litters of from three to six young each year. Squirrels have fewer and smaller litters. Why must the rabbit multiply more rapidly than the squirrel in order to survive? English rabbits have increased in Australia until they are a plague. Sheep raising is interfered with by the loss of grass. The Australians now ship them to England in cold storage for food. Rabbits and most rodents lead a watchful, timid, and alert life. An exception is the porcupine, which, because of the defense of its barbed quills, is dull and sluggish.

The common rodents are:--

squirrels rabbits rats mice beavers muskrats porcupines guinea pig pouched gopher prairie dog prairie squirrel chipmunk ground hog field mouse

Which of the above rodents are commercially important? Which are injurious to an important degree? Which have long tails? Why? Short tails? Why? Long ears? Why? Short ears? Why? Which are aquatic? Which dig or burrow? Which are largely nocturnal in habits? Which are arboreal? Which are protected by coloration? Which escape by running? By seeking holes?

=Economic Importance.=--Rabbits and squirrels destroy the eggs and young of birds. Are rabbits useful? Do they destroy useful food? The use of beaver and muskrat skins as furs will probably soon lead to their extinction. Millions of rabbits’ skins are used annually, the hair being made into felt hats. There are also millions of squirrel skins used in the fur trade. The hairs of the tail are made into fine paint brushes. The skins of common rats are used for the thumbs of kid gloves. _Order_ ____. _Why?_ ____.

[Illustration: FIG. 375.--FLYING SQUIRREL (_Pteromys volucella_). × ¹⁄₄.]

=Elephants.=--Elephants, strange to say, have several noteworthy resemblances to rodents. Like them, elephants have no canine teeth; their molar teeth are few, and marked by transverse ridges and the incisors present are prominently developed (Figs. 376, 377). Instead of four incisors, however, they have only two, the enormous tusks, for there are no incisors in the lower jaw. Elephants and rodents both subsist upon plant food. Both have peaceful dispositions, but one order has found safety and ability to survive by attaining enormous size and strength; the other (_e.g._ rats, squirrels) has found safety in small size. Explain.

Suppose you were to observe an elephant for the first time, without knowing any of its habits. How would you know that it does not eat meat? That it does eat plant food? That it can defend itself? Why would you make the mistake of thinking that it is very clumsy and stupid? Why is its skin naked? Thick? Why must its legs be so straight? Why must it have either a very long neck or a substitute for one? (Fig. 376.) Are the eyes large or small? The ears? The brain cavity? What anatomical feature correlates with the long proboscis? Is the proboscis a new organ not found in other animals, or is it a specialization of one or more old ones? Reasons? What senses are especially active in the proboscis? How is it used in drinking? In grasping? What evidence that it is a development of the nose? The upper lip?

[Illustration: FIG. 376.--HEAD OF AFRICAN ELEPHANT.]

[Illustration: FIG. 377.--MOLAR TOOTH OF AFRICAN ELEPHANT.]

The tusks are of use in uprooting trees for their foliage and in digging soft roots for food. Can the elephant graze? Why, or why not? There is a finger-like projection on the end of the snout which is useful in delicate manipulations. The feet have pads to prevent jarring; the nails are short and hardly touch the ground. _Order_ ____. _Why?_ ____. Key, page 193.

=Whales, Porpoises, Dolphins.=--As the absurd mistake is sometimes made of confusing _whales_ with fish, the pupil may compare them in the following respects: eggs, nourishment of young, fins, skin, eyes, size, breathing, temperature, skeleton (Figs. 209, 379, and 397).

[Illustration: FIG. 378.--HARPOONING GREENLAND WHALE (see Fig. 351).]

_Porpoises and dolphins_, which are smaller species of whales, live near the shore and eat fish. Explain the expression “blow like a porpoise.” They do not exceed five or eight feet in length, while the deep-sea whales are from thirty to seventy-five feet in length, being by far the largest animals in the world. The size of the elephant is limited by the weight that the bones and muscles support and move. The whale’s size is not so limited.

The _whale_ bears one young (rarely twins) at a time. The mother carefully attends the young for a long time. The _blubber_, or thick layer of fat beneath the skin, serves to retain heat and keep the body up to the usual temperature of mammals in spite of the cold water. It also serves, along with the _immense lungs_, to give lightness to the body. Why does a whale need large lungs? The _tail of a whale_ is horizontal instead of vertical, that it may steer upward rapidly from the depths when needing to breathe. The _teeth_ of some whales do not cut the gum, but are reabsorbed and are replaced by horny plates of “whalebone,” which act as strainers. Give evidence, from the flippers, lungs, and other organs, that the whale is descended from a land mammal (Fig. 397). Compare the whale with a typical land mammal, as the dog, and enumerate the specializations of the whale for living in water. What change took place in the general form of the body? It is believed that on account of scarcity of food the land ancestors of the whale, hundreds of thousands of years ago, took to living upon fish, etc., and, gradually becoming swimmers and divers, lost the power of locomotion on land. _Order_ ____. _Why?_ ____.

[Illustration: FIG. 379.--DOLPHIN.]

Elephants are rapidly becoming extinct because of the value of their ivory tusks. Whales also furnish valuable products, but they will probably exist much longer. Why?

The =manatees and dugongs= (sea cows) are a closely related order living upon water plants, and hence living close to shore and in the mouths of rivers. _Order_ ____. _Why?_ ____.

[Illustration: FIG. 380.--MANATEE, or sea cow; it lives near the shore and eats seaweed. (Florida to Brazil.)]

=Hoofed Mammals.=--All the animals in this order walk on the tips of their toes, which have been adapted to this use by the claws having developed into _hoofs_. The order is subdivided into the _odd-toed_ (such as the horse with one toe and the rhinoceros with three) and the _even-toed_ (as the ox with two toes and the pig with four). All the even-toed forms except the pig and hippopotamus chew the cud and are given the name of _ruminants_.

=Horse and Man Compared= (Figs. 381, 399).--To which finger and toe on man’s hand and foot does the toe of a horse’s foot correspond? Has the horse kneecaps? Is its heel bone large or small? Is the fetlock on toe, instep, or ankle? Does the part of a horse’s hind leg that is most elongated correspond to the thigh, calf, or foot in man? On the fore leg, is the elongated part the upper arm, forearm, or hand? Does the most elongated part of the fore foot correspond to the finger, palm, or wrist? On the hind foot is it toe, instep, or ankle? Is the fetlock at the toe, instep, or heel? (Fig. 385.) Is the hock at the toe, instep, heel, or knee? _Order_ ____. _Why?_ ____.

[Illustration: FIG. 381.--Left leg of man, left hind leg of dog and horse; homologous parts lettered alike.]

=Specializations of the Mammals.=--The early mammals, of which the present marsupials are believed to be typical, had five toes provided with claws. They were not very rapid in motion nor dangerous in fight, and probably ate both animal and vegetable food.

[Illustration: FIG. 382.--SKELETONS OF FEET OF MAMMALS.

_P_, horse; _D_, dolphin; _E_, elephant; _A_, monkey; _T_, tiger; _O_, aurochs; _F_, sloth; _M_, mole.

=Question:= Explain how each is adapted to its specialized function.]

According to the usual rule, they tended to increase faster than the food supply, and there were continual contests for food. Those whose claws and teeth were sharper drove the others from the food, or preyed upon them. Thus the specialization into the bold flesh eating beasts of prey and the timid vegetable feeders began. Which of the flesh eaters has already been studied at length? The insectivora escaped their enemies and found food by learning to burrow or fly. The rodents accomplished the same result either by acquiring great agility in climbing, or by living in holes, or by running. The proboscidians acquired enormous size and strength. The hoofed animals found safety in flight.

[Illustration: _Equus_

_Protohippus_

_Pliohippus_

_Miohippus_

_Mesohippus_

_Orohippus_

FIG. 383.--Feet of the ancestors of the horse.]

[Illustration: FIG. 384.--TAPIR OF SOUTH AMERICA (_Tapirus americanus_). × ¹⁄₂₅.

=Questions:= How does it resemble an elephant? (Fig. 376.) A horse? (p. 210.)]

[Illustration: FIG. 385.--HORSE, descended from a small wild species still found in Western Asia.]

=Ungulates=, as the horse, need no other protection than their great speed, which is due to lengthening the bones of the legs and rising upon the very tip of the largest toe, which, to support the weight, developed an enormous toe-nail called a hoof. The cattle, not having developed such speed as the horse, usually have horns for defense. If a calf or cow bellows with distress, all the cattle in the neighborhood rush to the rescue. This unselfish instinct to help others was an aid to the survival of wild cattle living in regions infested with beasts of prey. Which of Æsop’s fables is based upon this instinct? The habit of rapid grazing and the correlated habit of chewing the cud were also of great value, as it enabled cattle to obtain grass hurriedly and retire to a safe place to chew it. Rudiments of the upper incisors are present in the jaw of the calf, showing the descent from animals which had a complete set of teeth. The rudiments are absorbed and the upper jaw of the cow lacks incisors entirely, as they would be useless because of the cow’s habit of seizing the grass with her rough tongue and cutting it with the lower incisors as the head is jerked forward. This is a more rapid way of eating than by biting. Which leaves the grass shorter after grazing, a cow or a horse? Why? Grass is very slow of digestion, and the ungulates have an alimentary canal twenty to thirty times the length of the body. Thorough chewing is necessary for such coarse food, and the ungulates which chew the cud (ruminants) are able, by leisurely and thorough chewing, to make the best use of the woody fiber (cellulose) which is the chief substance in their food.

[Illustration: FIG. 386.--SKELETON OF COW. Compare with horse (Fig. 395) as to legs, toes, tail, mane, dewlap, ears, body.]

=Ruminants= have four divisions to the stomach. Their food is first swallowed into the roomy _paunch_ in which, as in the crop of a bird, the bulky food is temporarily stored. It is not digested at all in the paunch, but after being moistened, portions of it pass successively into the _honeycomb_, which forms it into balls to be belched up and ground by the large molars as the animal lies with eyes half closed under the shade of a tree. It is then swallowed a second time and is acted upon in the third division (or _manyplies_) and the fourth division (or _reed_). Next it passes into the intestine. Why is the paunch the largest compartment? In the figure do you recognize the paunch by its size? The honeycomb by its lining? Why is it round? The last two of the four divisions may be known by their direct connection with the intestine.

[Illustration: FIG. 387.--Food traced through stomachs of cow. (Follow arrows.)]

[Illustration: FIG. 388.--Section of cow’s stomachs. Identify each. (See text.)]

[Illustration: FIG. 389.--OKAPI. This will probably prove to be the last large mammal to be discovered by civilized man. It was found in the forests of the Kongo in 1900.

=Questions:= It shows affinities (find them) with giraffe, deer, and zebra. It is a ruminant ungulate (explain meaning--see text).]

The true _gastric juice_ is secreted only in the fourth stomach. Since the cud or unchewed food is belched up in balls from the round “honeycomb,” and since a ball of hair is sometimes found in the stomach of ruminants, some ignorant people make the absurd mistake of calling the ball of hair the cud. This ball accumulates in the paunch because of the friendly custom cows have of combing each other’s hair with their rough tongues, the hair sometimes being swallowed. Explain the saying that if a cow stops chewing the cud she will die.

[Illustration: FIG. 390.--AFRICAN CAMEL (_Camelus dromedarius_).]

Does a cow’s lower jaw move sidewise or back and forth? Do the ridges on the molars run sidewise or lengthwise? Is a cow’s horn hollow? Does it have a bony core? (Fig. 344.)

[Illustration: FIG. 391.--PRONG-HORNED ANTELOPE (_Antelocarpa Americana_). Western states.]

The permanent hollow horns of the cow and the solid deciduous horns of the deer are typical of the two kinds of horns possessed by ruminants. The prong-horned antelope (Fig. 391) of the United States, however, is an intermediate form, as its horns are hollow, but are shed each year. The hollow horns are a modification of hair. Do solid or hollow bones branch? Which are possessed by both sexes? Which are pointed? Which are better suited for fighting? Why would the deer have less need to fight than the cattle? Deer are polygamous, and the males use their horns mostly for fighting each other. The sharp hoofs of deer are also dangerous weapons. The white-tail deer (probably the same species as the Virginian red deer) is the most widely distributed of the American deer. It keeps to the lowlands, while the black-tailed deer prefers a hilly country. The moose, like the deer, browses on twigs and leaves. The elk, like cattle, eats grass.

[Illustration: FIG. 392.--ROCKY MOUNTAIN SHEEP (_Ovis montana_). × ¹⁄₂₄.]

The native sheep of America is the big horn, or Rocky Mountain sheep (Fig. 392). The belief is false that they alight upon their horns when jumping down precipices. They post sentinels and are very wary. There is also a native goat, a white species, living high on the Rocky Mountains near the snow. They are rather stupid animals. The bison once roamed in herds of countless thousands, but, with the exception of a few protected in parks, it is now extinct. Its shaggy hide was useful to man in winter, so it has been well-nigh destroyed. For gain man is led to exterminate elephants, seals, rodents, armadillos, whales, birds, deer, mussels, lobsters, forests, etc.

[Illustration: FIG. 393.--PECCARY (_Dicotyles torquatus_) of Texas and Mexico. × ¹⁄₁₂.]

Our only native hog is the peccary, found in Texas (Fig. 393). In contrast with the heavy domestic hog, it is slender and active. It is fearless, and its great tusks are dangerous weapons. The swine are the only ungulates that are not strictly vegetable feeders. The habit of fattening in summer was useful to wild hogs, since snow hid most of their food in winter. The habit has been preserved under domestication. Are the small toes of the hog useless? Are the “dew claws” of cattle useless? Will they probably become larger or smaller? _Order?_

[Illustration: =Illustrated Study=

FIG. 394.--BIRD.

FIG. 395.--HORSE.

FIG. 396.--OX.

FIG. 397.--DOLPHIN.

FIG. 398.--FISH.]

[Illustration: =Illustrated Study=

FIG. 399.--MAN.

FIG. 400.--CHIMPANZEE. (See Fig. 406.)]

=Illustrated Study of Vertebrate Skeletons=: Taking man’s skeleton as complete, which of these seven skeletons is most incomplete?

Regarding the fish skeleton as the original vertebrate skeleton, how has it been modified for (1) walking, (2) walking on two legs, (3) flying?

Which skeleton is probably a degenerate reversion to original type? (p. 209.)

How is the horse specialized for speed?

Do all have tail vertebræ, or vertebræ beyond the hip bones? Does each have shoulder blades?

Compare (1) fore limbs, (2) hind limbs, (3) jaws of the seven skeletons. Which has relatively the shortest jaws? Why? What seems to be the typical number of ribs? limbs? digits?

Does flipper of a dolphin have same bones as arm of a man?

How many thumbs has chimpanzee? Which is more specialized, the foot of a man or a chimpanzee? Is the foot of a man or a chimpanzee better suited for supporting weight? How does its construction fit it for this?

Which has a better hand, a man or a chimpanzee? What is the difference in their arms? Does difference in structure correspond to difference in use?

Which of the seven skeletons bears the most complex breastbone?

Which skeleton bears no neck (or cervical) vertebræ? Which bears only one?

Are all the classes of vertebrates represented in this chart? (p. 125.)

[Illustration: FIG. 401.--SACRED MONKEY OF INDIA (_Semnopithecus entellus_). × ¹⁄₁₂.]

=Monkeys, Apes, and Man.=--Study the figures (399, 400); compare apes and man and explain each of the differences in the following list: (1) feet, three differences; (2) arms; (3) brain case; (4) jaws; (5) canine teeth; (6) backbone; (7) distance between the eyes.

[Illustration: FIG. 402.--LEMUR (_Lemur Mongoz_). × ¹⁄₁₀. Which digit bears a claw?]

_A hand_, unlike a foot, has one of the digits, called a thumb, placed opposite the other four digits that it may be used in grasping. Two-handed man and four-handed apes and monkeys are usually placed in one order, the _Primates_, or in two orders (see table, page 193). The lowest members of this order are the _lemurs_ of the old world. Because of their hands and feet being true grasping organs, they are placed among the primates, notwithstanding the long muzzle and expressionless, foxlike face. (Fig. 402.) Next in order are the _tailed monkeys_, while the _tailless apes_ are the highest next to man.

[Illustration: FIG. 403.--BROAD-NOSED MONKEY. × ¹⁄₁₀. America.]

[Illustration: FIG. 404.--NARROW-NOSED MONKEY. × ¹⁄₁₂. Old World.]

[Illustration: FIG. 405.--GORILLA. (Size of a man.)]

The _primates of the New World_ are all monkeys with long tails and broad noses. They are found from Paraguay to Mexico. The _monkeys and apes of the Old World_ have a _thin partition_ between the nostrils, and are thus distinguished from the monkeys of the New World, which have a _thicker partition_ and have a broader nose. (Figs. 403, 404.) The monkeys of America all have _six molar teeth_ in each half jaw (Fig. 352); the monkeys and apes of the Old World have thirty-two teeth which agree both in number and arrangement with those of man.

Which of the primates figured in this book appear to have the arm longer than the leg? Which have the eyes directed forward instead of sideways, as with cats or dogs?

Nearly all the primates are _forest dwellers_, and inhabit warm countries, where the boughs of trees are never covered with ice or snow. Their _ability in climbing_ serves greatly to protect them from beasts of prey. Many apes and monkeys are able to assume the upright position in walking, but they touch the ground with their knuckles every few steps to aid in preserving the balance.

[Illustration: FIG. 406.--CHIMPANZEE.]

The _Simians_ are the highest family of primates below man, and include the gorilla, chimpanzee, orang, and gibbon. Some of the simians weave together branches in the treetops to form a rude nest, and all are very affectionate and devoted to their young. How are apes most readily distinguished from monkeys? (Figs. 401, 406.)

The study of man as related to his environment will be taken up in detail in the part called Human Biology. We will there examine the effect upon man’s body of the rapid changes since emerging from savagery that he has made in food eaten, air breathed, clothing, and habits of life.

[Illustration: FIG. 407.--ANATOMY OF RABBIT.

_a_, incisor teeth; _b_, _b′_, _b″_, salivary glands; _k_, larynx; _l_, windpipe; _c_, gullet; _d_, diaphragm (possessed only by mammals); _e_, stomach; _g_, small intestine; _h_, _h′_, large intestine; _f_, junction of small and large intestine; _g_, _g′_, cæcum, or blind sac from _f_ (corresponds to the shrunken rudimentary vermiform appendix in man); _m_, carotid arteries; _n_, heart; _o_, aorta; _p_, lungs; _q_, end of sternum; _r_, spleen; _s_, kidney; _t_, ureters (from kidney to bladder _v_). 2 brain of rabbit: _a_, olfactory nerves; _b_, cerebrum; _c_, midbrain; _d_, cerebellum.]

=Table for Review=

==============+=======+=======+=======+=======+=======+=======+======= | FISH | FROG | TURTLE| BIRD | CAT | HORSE | MAN --------------+-------+-------+-------+-------+-------+-------+------- | | | | | | | Names of limbs| | | | | | | | | | | | | | --------------+-------+-------+-------+-------+-------+-------+------- | | | | | | | Acutest sense | | | | | | | | | | | | | | --------------+-------+-------+-------+-------+-------+-------+------- | | | | | | | Digits on fore| | | | | | | and hind limb | | | | | | | | | | | | | | --------------+-------+-------+-------+-------+-------+-------+------- | | | | | | | Locomotion | | | | | | | | | | | | | | --------------+-------+-------+-------+-------+-------+-------+------- | | | | | | | Kind of food | | | | | | | | | | | | | | --------------+-------+-------+-------+-------+-------+-------+------- | | | | | | | Care of young | | | | | | | | | | | | | | ==============+=======+=======+=======+=======+=======+=======+=======

[Illustration:

St. Bernard Eskimo Poodle Dachshund

German mastiff English bloodhound

Pointer Bulldog Greyhound

Newfoundland Shepherd Spitz

FIG. 408.--ARTIFICIAL SELECTION. Its effects in causing varieties in one species. Which of the dogs is specialized for speed? Driving cattle? Stopping cattle? Trailing by scent? Finding game? Drawing vehicles? Going into holes? House pet? Cold weather? In Mexico there is a hairless dog specialized for hot climates. The widely differing environments under various forms of domestication cause “sports” which breeders are quick to take advantage of when wishing to develop new varieties. Professor De Vries by cultivating American evening primroses in Europe has shown that a sudden change of environment may cause not only varieties but new species to arise.]

HUMAN BIOLOGY