EVIDENCE FROM COMPARATIVE ANATOMY 53 



throughout. As this group or that advanced in 

 differentiation certain appendages became specialized 

 for the better performance of particular operations. 



In the crabs may be observed a higher grade of 

 organization than in the lobsters, for the crabs, at 

 first sight, appear to have lost the tail entirely. 

 Turning a crab on its back, however, the segmented 

 tail is seen to be folded under the body and lying 

 in a groove on the ventral surface; the appendages 

 of the tail have been almost completely suppressed. 



Even more remarkable is the series of modifica- 

 tions brought to light by a comparative study of 

 the mouth-parts among the insects, in which far- 

 reaching modifications have been brought about in 

 adaptation to different kinds of food and different 

 habits of life. Fundamentally, the parts are the 

 same throughout, but the transformation is fre- 

 quently so profound as to obscure this fact. In 

 insects, such as the cockroach, which live upon solid 

 food, there are masticating jaws; in the bumble bee 

 a licking apparatus; in the butterflies and moths a 

 long, tubular proboscis for sucking the nectar from 

 flowers; in the mosquito a most elaborate arrange- 

 ment for piercing the skin and sucking the blood of 

 its victim. "But always it is the same individual 

 parts, on the same definite segments, which are re- 

 peated according to rule as regards number and 

 form, but with a different mode of use; a pair of 

 upper jaws, a first and second pair of lower jaws, but 

 the latter may be long drawn out and rolled up in 



