1873.] 185 [McCrady. 



trumpet-shaped tube and the remainder of the ordinary oral-ana 

 opening, which we see in Siphonactinia, and less distinctly in Cerian- 

 thus, we must recollect that many Platyelminths and some Nematodes 

 are similarly deprived of an anus, and that the former, in many 

 points of their structure, recall the type of organs seen in Acalephae 

 though they present this type in a highly differentiated condition. 



The group of Vermes, even as generally received, and excluding 

 the Echinodermata, appears to me a heterogeneous collection of re- 

 markable forms, some of which can hardly be said to have any close 

 homologies with the others, and to agree with them in little else than 

 a general vermiform appearance, and the possession of some similar 

 structures, which may prove to have no closer relations with each 

 other than the arms of Brachiopoda with the gills of Fishes, or the 

 fin-like organs of Loligo with those of Amphioxus. The «Annulata 

 or Annelida and Rotatoria have the closest affinities with the Arthro- 

 podous Articulates. The Gephyrian Vermes have undoubted and 

 long recognized connections with the Echinoderms, and these, with 

 embryological considerations, have induced Huxley to associate the 

 latter with the Annulata. But there is another view which may 

 give quite a different result without separating the Gephyrians from 

 the Echinoderms; I mean the view that the Gephyrians are an aber- 

 rant outlying branch of the Radiate, as the Cirrhipeds are of the 

 Articulate, and the Chitonidae and Dentalium of the Molluscan type. 

 The very larvae of the Echinoderms which have furnished the argu- 

 ment for associating the latter with the Vermes, have really very 

 decided affinities with Ctenophorous Medusse, as Agassiz claimed, 

 and the typical affinities of the Acalephae with Echinoderms are so 

 close that any disposition made of the one group must eventually 

 carry the other along with it. 



Just as the Gephyrians probably constitute an aberrant group o 

 Echinodermata, the Platyelminths (Trematodes, Turbellarians and 

 Cestodes), may constitute another such aberrant group with more 

 or less affinities with the Acalephae, especially the Ctenophoras. 

 The question whether Cuvier, mistaken though he was as to the true 

 affinities of the Polyzoa, the Rotatoria, and most of the other organ- 

 isms included in the provisional group of Infusoria, had not, never- 

 theless, a more just conception of the limits of the morphological 

 possibilities of the type which he not very happily named Radiata, 

 than his successors, is yet an open one; and a thorough discussion 

 of it must be had before we can accept the Vermes as anything 



