The Clythrae 



whose maintenance is a more delicate matter, 

 covers itself with feathers, which overlap 

 evenly, and puts round its body a thick cush- 

 ion of air on a bed of down. It has on its 

 tail a pot of cosmetic, a bottle of hair-oil, a 

 fatty gland from which the beak obtains an 

 ointment wherewith it preens the feathers one 

 by one and renders them impermeable to 

 moisture. A great expender of energy by 

 reason of the exigencies of flight, it is es- 

 sentially, chilly creature that it is, better- 

 adapted than any other to the retention of 

 heat. 



For the slow-moving reptile the scales suf- 

 fice, preserving it from hurtful contacts, but 

 playing hardly any part as a bulwark against 

 changes of temperature. 



In its liquid environment, which is far 

 more constant than the air, the fish requires 

 no more. Without effort on its part, with- 

 out violent expenditure of motor force, the 

 swimmer is borne up by the mere pressure of 

 the water. A bath whose temperature 

 varies but little enables it to live in ignorance 

 of excessive cold or heat. 



In the same way, the mollusc, for the most 

 part a denizen of the seas, leads a blissful 

 life in its shell, which is a defensive fortress 



449 



