MAMMALIA. 3 



The species of the Mammalia vary in tlieir forms accordino- to 

 the uses which the animals have to make of them. Nearly all 

 of the Mammalia have four limbs. The Cetacea have no abdominal 

 members, and their anterior members are formed 'like fins or 

 paddles for swimming. 



The organs of sense are generally more developed in this class of 

 animals than in all those we have hitherto studied. The sense of 

 touch, which is almost wanting in some — as the Horse and the Ox 

 — because their extremities are covered by hoofs, is very highly 

 developed in Monkeys. "With these animals, the U2)per member is 

 tei-minated by an organ of prehension, which can in a manner 

 mould itself on the objects it takes hold of, and which impai'ts to 

 the sense of touch an enhanced delicacy. The sense of vision alone 

 is highest in the class of Birds. 



The seeing ajiparatus is, in general, more developed in the 

 Mammalia that j)rowl by night, than in those which seek their 

 food by day. Some which, like the Moles, live underground, have 

 excessively small eyes, over which the skin is merely attenuated in 

 certain species of Mole, there being no visual aperture whatever. 



Very highly developed in carnivorous animals, the sense of 

 smell is generally less developed in the other classes of Mammalia- 

 It is acute in the Euminantia and in the Solipodes. 



The more timid and the weaker the animal, the finer is its sense 

 of hearing. This sense, moreover, undergoes great variations in 

 the Mammalia. In aquatic Mammalia, it is comparatively dull, 

 with some exceptions (p. 35). 



The taste differs equ.ally, according as the Mammalia are her- 

 bivorous, insectivorous, or carnivorous. 



The muscular system depends on the form and manner of loco- 

 motion and on the length of the animal. 



The nervous system among the animals of this class only diff'ers 

 by having certain of its anatomical elements more or less developed. 

 In general, the brain is sufficiently voluminous, and increases in 

 size in proportion as the animal rises in the organic scale. 



The functions of nutrition are performed in the same manner in 

 nearly all the Mammalia ; so that the digestive organs vary but 

 very little in this great class. 



The upper orifice of the digestive tube, or the month, is mostly 

 provided with teeth, the form of which depends on the food upon 



b2 



