ENTOPROCTA. 571 



and the tentacles and a new opening for the vestibule are established. 

 During the whole of this process the alimentary tube, with its 

 mouth and anus, persist. 



Here then is a metamorphosis very similar in its results to^the 

 process which takes place in the Ectoprocta, viz., an entire shifting of 

 the oral surface round to the opposite side of the larva ; but differing 

 from that, in the fact (1) that the attachment is effected by the edge 

 of the ventral* surface, and not by an adhesive organ between the 

 mouth and anus, and (2) that the larval organs do not undergo 

 disruption, but allow us to perceive that the alteration is due to the 

 relative growth of the parts rather than to the formation of a new 

 mouth and anus on the aboral side of the larva. 



As to the actual relations between this larva and the Cyphonautes, 

 they appear to resemble one another very nearly, but on a critical 

 examination certain points of difference become obvious. These are 

 (1) the absence in the Entoproct larva of an adhesive organ ; (2) the 

 presence of a rudiment of the cerebral ganglion (dorsal organ), and 

 (3) the absence of the pyriform organ in the Entoproct larva. The 

 pyriform organ, which has been supposed to have something to do 

 with the cerebral ganglion, t cannot be homologous with the dorsal 

 organ of Entoprocta, because it is within the velar circlet. So that, 

 on the whole, we are inclined to think that the resemblances between 

 these larvae are superficial ones, and cannot be used as important 

 arguments in favour of the view that the Polyzoa constitute a 

 monophyletic group. On the other hand, it is held by many 

 zoologists that the Ectoprocta and Entoprocta should not be 

 associated in the same group, and that there is really no close 

 relationship between them. The principal argument used in favour 

 of this contention is that the Entoprocta are without a coelom, 

 and should be removed altogether from the Coelomata. This view 

 of the matter is further borne out by the relations of the gonads 

 and the presence of the two ciliated excretory canals. We, however, 

 while admitting that there is much to be said for it, do not regard 

 it as proven, and cannot give it expression in this work. 



The comparison which Caldwell has instituted between Phoronis and the 

 Polyzoa is based upon the supposed resemblance between Phoronis and the 



* This attachment must have been confined to the anterior side of the ventral 

 edge, otherwise it is impossible to conceive how the process of relative shifting 

 of the mouth and anus above described in its abbreviated embryonic form 

 could have happened in the ancestral history, 



t The cerebral ganglion on the view here adopted of the Ectoprocta is not, of 

 course, present in the adult, for as pointed out above, the ganglion of the 

 Ectoprocta, though sometimes called dorsal, must be really suboesophageal. 



