CLASS MAMMALS. 



345 



of animals which gives as much in the way of successful 

 parental care to the young. Because of this the higher 

 mammals bring forth fewer young in a lifetime than any 

 other class of animals. 



339. Library Exercise: a Comparison of Monotremes, Marsupials, 

 and Placentals. By liberal use of the reference books, and in parallel 

 columns, make a contrast of the three divisions of mammals in 

 respect to the following particulars: Their geographical distri- 

 bution; their peculiarities of structure; the eggs, and their size and 

 structure; the gestation or internal development; the peculiarities 

 of the brain. 



340. Field Exercise : An Enumeration of the Domestic Species, 

 and of the Native Wild Species of Mammals of Your Community. 



Seek to get a complete list of these mammals, and put in groups 

 those that seem most similar to you, enumerating the grounds for 

 your classification. In doing this get together all the facts you 

 know in respect to the following points: the general mode of life; 

 the foods used and the manner of getting it ; the size and form of the 

 body; the character of the jaws and teeth; the form and size of 

 legs and the character of the toes ; the powers and special methods of 

 locomotion; the external covering; mating habits; the number of 

 young at a birth; the mammary glands, their number and position; 

 the methods of caring for the young ; the social habits ; special organs, 

 as horns, tusks, and the like; their bearing on human welfare. 



341. The Nervous System and the Mental Qualities of 

 Mammals. The brain of mammals, especially the fore- 

 brain or cerebral hemispheres, is of relatively large size. 

 In the placentals this part of the brain, instead of being 

 smooth like that of the birds, has folds or convolutions 

 which increase the amount of its outer surface (Fig. 155) . 

 This outer surface is especially rich in the nervous cells, 

 or "gray matter," and the intelligence of animals is 

 roughly proportional to the amount of these cells. 



The mammals have all the senses that the other verte- 

 brates have, and these are well developed on the whole, 

 although they are unequally perfect in the various types. 



