IOO EVOLUTION OF TO-DAY. 



tology. At the beginning of our record of life, the 

 world was not filled with a few generalized types, 

 but with an already well-differentiated fauna of 

 genera and species. For instance : the Echinoderms, 

 instead of consisting of a few generalized types, were 

 already divided into the perfectly distinct orders, 

 Crinoids, Blastids, Cystids, Asteroids, Ophiuroids, 

 and Echnoids. All had their special genera and 

 species, and almost none of them such as can be 

 imagined to have given rise to the groups of later 

 times. 



This claim is, however, partially a misunderstand- 

 ing, for it seems to imply that we should expect to 

 find animals which were purely generalized, with no 

 specific characters. The most comprehensive types 

 which ever existed must have had, along with their 

 general characteristics, their own special features, 

 which adapted them to surroundings. While they 

 would be synthetic in that they shared the char- 

 acters of many different forms, each one would 

 also be distinctly specialized. No animal could ex- 

 ist without having definite shape, size, color, etc., 

 and these characters would be specific. It is, then, 

 not at all surprising that we find even in the Silurian 

 a specialized fauna and flora, for it could not have 

 been otherwise. And, moreover, it is perfectly in- 

 telligible that some of the simple groups, even at 

 that early date, could have become highly special- 

 ized, as highly, in fact, as they became afterwards. 

 The force of the difficulty here, as far as it is a diffi- 

 culty, lies not in the presence of specific distinctions, 

 but in the absence of generalized characteristics. 



