124 



praeoral cavity, as shewn in Hatschek's fig. 145, suggest that the ventral cavity may correspund 

 with that part of the anterior body-cavity of Cephalodiscjis which hes in the proboscis-stalk, 

 ventrally to the notochord; and that in fact the proboscis in Amphioxus is represented only 

 by a part of the proboscis-stalk. It would be interesting to know more of the nature of van 

 Wijhe's dorsal praeoral cavity ("Schnauzenhöhle"); and it is conceivable that it might be the 

 homolocrue of the pericardium of the Enteropneusta. 



The only group with regard to which it appears necessary to say more is that of the 

 Polyzoa. A large number of writers have assumed — and it appears to me on inadequate 

 grounds — that Phoronis is related to the Polyzoa. If Phoronis be so related, it is not foreign 

 to the object of this memoir to consider the question in its hearings on Cephalodisciis. 



It may be remembered at the outset that on the occasion of the first discovery ot 

 Rhabdopleiira by Sars and Norman, no doubt was entertained of the correctness of the view that 

 this animal was an aberrant Polyzoon. The later discovery of Cephalodisciis, and its association 

 with Rhabdopleura, naturally led to the same view being adopted with regard to the subject 

 of this Report. With the discovery that Ccphalodiscus has affinities in the direction of Balano- 

 glossus, it appeared reasonable to remove it from the Polyzoa, since these animals had not been 

 shewn to possess any of the characters which specially connect Cephalodisciis with Balanoglossus. 

 What holds good for Cephalodisciis must, I think, also apply to Rhabdopleura. 



In again taking ujj the study of Cephalodisciis I have seen no sufficiënt reason for 

 modifying the views I formerly expressed (87) with regard to this question. It might indeed be 

 maintained that the embryo of C gracilis with its large internal yolk-mass, its conspicuous 

 ventral invagination of ectoderm and its "pyriform organ" was directly comparable with the 

 larva of one of the marine Ectoproctous Polyzoa. To this might perhaps be added the fact 

 (if it be a fact) that in both groups the alimentary canal of the bud is developed entirely trom 

 an invagination of the outer layer. 



It remains to be seen whether the later developmental history of Cephalodisciis will throw 

 any further light on this particular question ; but for my own part I do not anticipate that it 

 will tend to strengthen the view that the Pterobranchia are allied to the Polyzoa. In order to 

 accept this view it is necessary either to regard the Ectoprocta as the most primitive of the 

 Polyzoa, or to take the view — which is adopted by Korschelt and Heider in their well 

 known text-book of Embryology — that the Ectoprocta have no close affinity to the Entoprocta. 

 It appears to me that this view is untenable, and I ma)- fortif)- my own opinion by quoting 

 that of Prouho '), the excellence of whose work in both subdivisions entitles him to speak with 

 authority, that " Aujourd'hui, aucun des zoologistes qui étuchent les Bryozoaires ne met en doubte 

 "Ie bien fondé des vues de Nitsche" [to the effect that the Entoprocta and the Ectoprocta are 

 two groups belonging to the same phylum]. The Entoprocta, on this view, furnish many clues 

 to the understanding of the Ectoprocta. In particular, the comparative study of the development, 

 taking into account such questions as the structure of the larvae of Entoprocta, the metamorphosis 

 of Pedicellina^ and the structure of Cyphonaiites appears to me to shew that the Polyzoa, as 



i) H. Prouho, "Contribution a FHistoire des Bryozoaires", Arch. Zool. Exp. et C.éii. (2) X, 1892, p. 641 



