182 RAYMOND C. OSBURN Vol. XXII, No. 7 



But what we are especially concerned with in this discussion 

 is progressive evolution in the sense that advances are made in 

 the direction of complexity and the origin of what we are 

 disposed to call higher animals, though we may be guilty of an 

 anthropocentrism in so doing. From the standpoint of the 

 Protozoan we might be considered degenerate, from the fact 

 that our cells have lost their capacity for independent life, and 

 have to live together or not at all. However, it is just this 

 very loss of independence of the individual cell, involving the 

 .principle of division of labor and necessitating specialization 

 for the better performance of some process and the co-operation 

 of various parts, that has marked the advance of more complex 

 organisms, whether we may be allowed to call them higher 

 or not. 



But variations may occur in all directions and it has often 

 happened that the road to adaptation has lain in the direction 

 of secondary simplification of structure, and selection, in such 

 cases, means the elimination of the more complex, in order 

 to adjust the animal more closely to its environment. 



The crayfishes of our American caverns have lost their 

 eyes, but they are highly adapted to a life in total darkness; 

 the sessile ascidians lose nearly all semblance to vertebrate 

 animals, which they clearly possess in the larval stage, by their 

 adaptation to sessile life; the whales and seacows have lost the 

 hind limbs and have taken on a fish-like form in adaptation 

 to aquatic existence. Among parasitic forms we see this 

 carried to the extreme. The tape- worm lacks entirely the 

 intestinal tract, and the parasitic barnacle Rhizocephala is so 

 profoundly degenerated that were it not for our knowledge 

 of its development we would not be able to state even its 

 affinities to the Crustacea. These degenerative changes, bring- 

 ing about the loss of simplification of structures, are just as 

 much the product of evolution as are the modification of a 

 fore limb to a wing in the bird, the highly organized mammalian 

 brain, or the complex social life of bees and ants. As Thomson 

 remarks, "It is plain that evolution may be down as well as up, 

 and that the gates of parasitism and other facile slopes of 

 degenerate life are always open. The tapeworm in its inglorious 

 ease is as much an outcome of evolution as the lark at heaven's 

 gate. " 



