Evolution of Animals 503 



Another advantage that can be claimed for the above pedi- 

 gree is that it is at once condensed and fairly continuous 

 in morphological advance and specialization. Balanoglossus, 

 Megalocercus of the tunicates, Amphioxus, and the Reptilia 

 are all of high interest and show us how life modifications have 

 often occurred. But all of them seem to be side developments 

 of minor value alongside the more direct, condensed, and now 

 dominant line. 



It follows however from this that, were a diagram made 

 of the zoological tree which would include living and fossil 

 species, while the main trunk would be relatively condensed 

 and low, the lateral branches would be enormously extended 

 and ramified. Next chapter will be devoted to consideration 

 of the connection of the main branches with the stem, and 

 therefrom the zoological tree as above suggested will be con- 

 structed. 



A striking and far-reaching principle is illustrated in the 

 above history, which may be synopsized in the classic and 

 trite sentence "the race is not to the swift, nor the battle to 

 the strong"; but it is to those who become the most adaptable, 

 the most responsive, the most plastic; in a sentence the most 

 highly, abundantly, and perfectly innervated. So the elon- 

 gated soft-bodied, ciliated, proboscis-stimulated, or cephalic- 

 brained and delicately skin-nerve-covered organisms have not 

 only survived; they have become the progressive and dominant 

 types. For through constant action of the environment, and 

 reaction of each succeeding organism that formed a link in 

 the long chain of animal life, slow but sure proenvironal out- 

 reaching unceasingly occurred, that ensured steady if slow 

 organization and advance in the chain of life. 



On the other hand, as not a few biologists of recent decades 

 have emphasized, the mailed, the shelled, the tusked, the 

 carnivorous, the fighting groui)s have survived for a season, 

 but one after another they have been exterminated amongst 

 themselves, or ha^"e failed to adapt themselves to changed 

 physical or biological environment. Softness, ])lasticity, corre- 

 lated nervous organization, and adaptability are and have been 

 leading characters in determining organic survival and advance. 



