570 ZOOLOGY. 



musical notes " (Martin ex Darwin). While quadrupeds 

 use their voices as alarm calls, most of the sounds are pro- 

 duced by the males, especially during the breeding season. 



Animals are mutually attracted or are individually pro- 

 tected from the attacks of other species by odors. The 

 scent-bags or odoriferous glands secreting a fluid differing 

 in consistency in different animals, are situated near the 

 base of the tail, as in the skunk, polecat, musk-deer, civet- 

 cat and allies, or they may be developed in the side of the 

 face, as in the male elephant, as well as sheep and goats. 

 The odor is either of musk or some form of it. The shrew- 

 mice, by reason of their odoriferous glands, are disliked and 

 consequently not hunted by birds. Universal deference is 

 paid to the skunk ; few dogs, and only those which are in- 

 experienced or peculiarly gifted, attacking them. The 

 males more usually emit a stronger odor than those of the 

 opposite sex. 



Some mammals have a summer and a winter pelage. The 

 hare, at the beginning of winter, doffs its summer coat for a 

 suit of white. The hibernation, or winter-sleep, is a re- 

 markable feature in the life of quadrupeds living in the 

 north temperate zone, such as the bear, dormouse, and bats. 

 During this period the temperature of their body falls, 

 respiration and circulation are lowered in the one case or 

 nearly ceases in the other, and life is sustained by the ab- 

 sorption of fat, which accumulates on the under side of the 

 neck in the so-called hybernation-glands. 



There are about 3500 species of mammals described, of 

 which 2100 are living ; of these 310 inhabit America north 

 of Mexico. Mammals live all over the earth's surface, but 

 mostly in the tropical region, those of the arctic zones having 

 been derived from the south since the end of the Tertiary 

 period. The range in space of certain species is very great 

 for example, the cougar, panther, or puma ranges from Brit- 

 ish to South America (Chili). The mammalian fauna of the 

 Tertiary deposits of the west was far more abundant than now, 

 the remains of over five hundred species having been already 

 discovered by Leidy, Cope, and Marsh in the few spots ex- 

 amined. The earlier (Eocene) mammals were generalized 



