410 



COMPARATIVE PHYSIOLOGY. 



The muscles of the skin, which either move it as a whole or 

 erect individual hairs, play an important part in modifying ex- 

 pression, well seen in the whole canine tribe and many others. 



There are several 

 modifications of the 

 sebaceousglands that 

 furnish highly odor- 

 iferous secretions as 

 in the civet cat, the 

 skunk, the musk- 

 deer, and many low- 

 er vertebrates. In 

 some, these are pro- 

 tective (skunk) ; in 

 others, though they 

 may not be agreeable 

 to the senses of man, 

 they are doubtless at- 

 tractive to the fe- 

 males of the same 

 tribe, and are to be 

 regarded as impor- 

 tant in "sexual se- 

 lection," being often 

 confined to the males 

 alone. 



Ear-wax and the 

 Meibomian secretion 

 are the work of 

 modified sebaceous 

 glands ; as also the 

 oil-glands so highly 

 developed in birds, 

 especially aquatic 

 forms, and of which 

 these creatures make 

 great use in preserv- 

 ing their feathers 

 from wetting. 



In our domestic 

 animals we may es- 

 pecially notice a cu 



Fig. 313.— Hair and hair-foUicle (after Sappey). 1, root 

 of hair; 2, bulb of bair: 3, internal root-slieatli; 5, 

 membrane of hair-follicle; 6, external membrane of 

 follicle; 7, 7, muscnlar bands attached to follicle; 

 8, 8, extremities of bands passing to skin; 9, com- 

 pound sebaceous gland, wim duct (10) opening mto 

 upper third of folucle ; U, simple sebaceous gland; 

 IS; opening of hair-follicle. 



