32 HOMOIOTHERMISM 



tions, (3) parental care of young, (4) migration, (5) 

 hibernation, (6) storing of food, (7) occupation of homes 

 which furnish more or less insulation, (8) the wearing 

 of clothes. 



Regulation of Body Temperature. — The regulation of 

 body temperature will be discussed in Chapter VIII and 

 hibernation in Chapter X. Many mammals protect their 

 young from adverse temperature conditions. New-born 

 rats and mice are unable for some days to resist changes 

 in atmospheric temperature. The human infant must be 

 protected for several weeks after birth and is easily 

 chilled by exposure to cold. The young of the marsupials 

 are carried in a pouch and are thus kept warm within 

 the mother's body. Among many species of birds the 

 young are kept warm by the heat from the mother for 

 some time following hatching. Apparently the mechan- 

 ism of temperature control is not completely functional 

 at the time of birth, even in the higher mammals. 



Migrations. — Many animals, notably the birds, mi- 

 grate during certain seasons of the year and thus escape 

 temperatures which might be deleterious. Migration, 

 however, is apparently not always brought about directly 

 by temperature variation and the advantage that may 

 be derived by migration as a means of protection against 

 extreme temperature changes is probably secondary to 

 those associated with the securing of food and repro- 

 duction. 



Morphological Adjustments. — Animals are provided 

 with certain morphological adaptations for restraining 

 the loss of heat through the skin. The more important 

 are: (1) the subcutaneous adipose tissue and (2) the 

 natural hairy or feathery coverings of the body. These 

 vary greatly in different environments and with the de- 

 gree of temperature fluctuations. The importance of the 



