EMBRYOLOGY AND CLASSIFICATION. 303 



life with characters peculiar to Radiates, and 

 ends it without assuming any feature of a higher 

 type. The Mollusk starts with a character es- 

 sentially its own, in no way related to the Ra- 

 diates, and never shows the least tendency to 

 deviate from it, either in the direction of the 

 Articulate or the Vertebrate types. This is 

 equally true, of the Articulates. At no stage of 

 growth are their young homologous to those of 

 Mollusks or Radiates any more than to those of 

 Vertebrates, and in their final development they 

 stand equally isolated from all others. That this 

 is emphatically true of the Vertebrates has already 

 been fully recognized ; and the facts known with 

 reference to this highest type of the Animal King- 

 dom might have served as a warning against the 

 loose statements still current concerning the so- 

 called infusorial condition of the young Inver- 

 tebrates. These results are of the highest impor- 

 tance at this moment, when men of authority in 

 science are attempting to renew the theory of a 

 general transmutation of all animals of the higher 

 types out of the lower ones. If such views are 

 ever to deserve serious consideration, and be ac- 

 knowledged as involving a scientific principle, it 

 will only be when their supporters shall have 

 shown that the fundamental plans of structure 

 characteristic of the primary groups of the Ani- 

 mal Kingdom are transmutable, or pass into one 



