16 PRIMITIVE ANIMALS 



when we attempt to go behind the phyla and dis- 

 cover their origin and inter-relationships, we leave 

 the firm ground altogether and wander in a slippery 

 and nebulous region of speculation. 



It is true that certain hypotheses of a plausible 

 character have been suggested which may have 

 satisfied uncritical minds, and which we often hear 

 advanced as a part of ascertained science and ac- 

 cepted in an otiose spirit. We are urged to believe 

 that life "originated" in certain chemical compounds 

 which on attaining a certain degree of complexity 

 began to exhibit the fundamental properties of life ; 

 that from these comparatively structureless masses 

 the nucleated cell was evolved and the unicellular 

 animals and plants, the Protozoa and Protophyta, 

 made their appearance ; that these gave rise to cell 

 colonies, the Metaphyta on the one hand, and the 

 Metazoa on the other. The Coelenterate type of 

 organization is presented to us as the form in which 

 the early Metazoa had their being, and from this by 

 the addition of the mesoderm we arrive at the 

 Platyhelmia, and from them by the addition of a 

 coelom and of metameric segmentation at the 

 segmented Annelid. And so by the addition and 

 subtraction of their characteristic qualities we may 

 pass in imagination from one fundamental type to 

 another ; but what is there of reality in these specu- 

 lations? They rest not on any objective evidence, 



