66 EMBRYOLOGY OF THE STARFISH. Part I, 



reminding us at once of the almost identical arrangement of an Echinoderm Piute us, 

 in the relations of the intestine to the stomach. The plutean forms certainly 

 show that the plan, upon which the Echinoderms are built, does not differ from 

 that upon which the Acalephs are built, and that we have between the Echinoderms 

 and Acalephs the same connection, based upon the identity of plan which exists 

 between the Acalephs and Polyps. We cannot, therefore, admit that the views so 

 frequently urged, and so universally admitted, in support of the separation of the 

 Acalephs and Polyps, as a distinct type (Ccelenterata), from the Echinoderms, 

 have any real foundation in nature; and still less can we concur in them, when 

 we remember that the main argument in their favor rests upon the assumed total 

 want of connection between the ambulacral system and the digestive system. Now 

 this connection has been shown, by Professor Agassiz, to exist in the adult of 

 many Echinoderms, while the facts above stated prove that it also exists in the 

 early stages of the embryonic development, when, in fact, the water-system is 

 formed from the digestive system. With this evidence falls the strongest argument 

 for the validity of a classification by which the type of Radiates would be broken 

 up, and the Polyps and Acalephs separated from the Echinoderms, as a distinct 

 type, under the name of Ccelenterata. We are, therefore, justified in affirming 

 that the type of Radiates constitutes an independent type of the animal kingdom, 

 containing three equivalent classes, — Echinoderms, Acalephs, and Polyps. 



