392 



GENERAL PRINCIPLES 



functional appendages, but in several species the appendages are 

 more or less rudimentary. In one the fore limbs are entirely 

 wanting, while the hind ones are greatly reduced. In still an- 

 other form there are no limbs at all, but both girdles are present. 

 In all these cases we have animals which are classed with quad- 

 rupedal forms, though they do not have four legs. The sig- 

 nificance of such rudimentary structures cannot be overlooked. 



Fig. 244. — The female luna-moth, Tropaea luna, seen from beneath. The 

 abdomen becomes so heavy before the eggs are deposited that the moth is 

 unable to fly. Xi. 



796. The young baleen whale has rudimentary teeth w^hich 

 never develop to a point where they can be of service to the 

 animal. In the middle of the upper surface of the skull of 

 many lizards there is a small opening. Over this place the skin 

 is transparent, and beneath there is an eye which is connected 

 with the fore brain by a long stalk. In the Cyclostomes there 



