676 COLLEGE ZOOLOGY 



retaining any small organisms that may have entered with the 

 water. 



The sulphur-bottom whale, Balcenoptera sulfureus. is the 

 largest whale, and the largest living animal, reaching a length 

 of ninety- five feet, and a weight of about 294,000 pounds; it 

 inhabits the Pacific from California to Central America. The 

 Greenland whale or bow-head, Baloena mysticctus, occurs in 

 polar seas; and reaches a length of about sixty feet. It yields 

 nearly three hundred barrels of oil, and about three thousand 

 pounds of the best whalebone. Baloenoptera musculus is a 

 sulphur-bottom whale occurring in the Atlantic and caught off 

 the coast of Newfoundland. , 



4. General Remarks on the Mammalia 



a. Integumentary Structures 



Hair. — The hairs that distinguish mammals from all other 

 animals are related phylogenetically to the feathers of birds and 

 the scales of reptiles. They are cornified modifications of the 

 epidermis (p. 403, Fig. 347, Se. SM) which project out from pits 

 in the skin, called hair follicles. The hair shaft (H) broadens at 

 the base, extending around a highly vascular papilla at the bot- 

 tom of the pit. When hairs are shed, new hairs usually arise to 

 take their place. Secretions from the sebaceous glands (D) keep 

 the hairs glossy. 



The two main types of hairs are (1) contour hairs which are 

 long and strong, and (2) woolly hairs which are shorter and con- 

 stitute the under fur. In some animals the woolly hairs have 

 a rough surface, as in the sheep, which causes them to cohere and 

 gives them their felting quality. Certain of the stronger hairs 

 may be moved by muscular fibers. The muscles of the dermis 

 are responsible for the erection of spines or the bristling of the 

 other hairs. 



Scales. — Scales are present on the bodies of a few mammals, 

 notably in the pangolin (Fig. 527) and on the tail of certain 

 rodents, such as the beaver, rats, and mice. 



