37 o COMPARATIVE ANATOMY AND PHYSIOLOGY. 



erection, they form very efficient organs of defence 

 and protection. 



Sometimes the hairs become specially endowed 

 with a tactile function, as in the " whiskers " of feline 

 and especially nocturnal carnivora ; reminding us so 

 far of the elongated delicate filaments of, no doubt, 

 similar functions, which are found on the bodies of 

 deep-sea fishes. 



The hairs may be greatly elongated, and used, as 

 in horses, for switches, by means of which their bodies 

 are freed from offending insects. 



The claws found on the digits of various lower 

 Vertebrates are, as " nails," almost constantly present 

 in Mammals, where they may be flat, as in man, sharp 

 offensive claws, as in Carnivora, large protecting hoofs, 

 as in Ungulates, or organs of support to arboreal 

 forms, such as the bat or the sloth ; they are wanting 

 in the Cetacea. 



The only Mammals in which long dermal scutes 

 are now developed are the armadillos (Fig. 157), where 

 three or more zones may be present, and form a more 

 or less complete protective covering for these animals ; 

 such scutes were present in enormous numbers in the 

 extinct Glyptodon and Hoplophorus. 



CHAPTER X. 



ORGANS OF MOVEMENT. 



IN the Protozoa, where division of labour never 

 proceeds so far as to lead to the formation of definite 

 tissues, the function of locomotion, like all the rest, 

 is simply performed by the protoplasm of the cell, 

 which, as we have already learnt, is contractile. 

 Thanks to this power of contractility, even an 



