MUSEUM OF COMPARATIVE ZOOLOGY. 103 



resent roughly a phylogenetic stage ancestral to both groups of Eryozoa, 

 but most clearly allied to adult Endoprocta. The formation of new ten- 

 tacles anteriorly and posteriorly in Figure 77, would reproduce the adult 

 Endoproct condition. Two changes load to the Ectoproct stage : first, 

 the closure of the tentacular corona posteriorly in front of the anus (Piute 

 V. Fig. 43), and, secondly, the formation of^he pharynx or anterior 

 part of the oesophagus by the growth of the oral tentacles over the floor 

 of the atrium towards the atrial opening. Thus the brain, which lies at 

 the floor of the atrium in Ectoprocta, comes to lie on the pharynx. The 

 pharynx would, upon this assumption, be a new structure, not found in 

 Endoprocta. Such appearances as are exhibited by Figure 77 lead me 

 to retract my former expressed opinion, in which I agreed with Xitsche in 

 saying that the earliest condition of the tentacular corona is a U-shaped 

 one. Rather, the tentacles are formed first on each side of the atrium, 

 and only secondarily grow around the mouth in front, as later they grow 

 in between mouth and anus. The U-shaped stage is therefore not the 

 primary one, but secondary. 



The close relationship of Endoprocta and Ectoprocta has recently been 

 doubted by Cori ('90, p. 16), but his chief argument depends upon the 

 dissimilarity of the Endoproct and Ectoproct kidney. Unfortunately, 

 our knowledge of the latter is still very imperfect, and we may well hope 

 for renewed researches in the subject by this skilful investigator. 



Ehlers ('90, pp. 149-154) has recently re-expressed his former ('7G, p. 

 132) utterances concerning the lack of homologj^ between the tentacles 

 of Ectoprocta and the " cirri" of Endoprocta. He finds the homologue 

 of the latter in the " Diaphragma" or " Kragen " of Ectoprocta. This is 

 the organ which I have believed to be homologous with Kraepelin's 

 "Randwulst" (which may be Anglicized as marginal thickening), — an 

 organ occurring in all Ectoprocta. It is nothing but the "neck of the 

 polypide," which has sunk below the general level of the body wall. It 

 is always provided with sphincter muscles, and in Ctenostomes forms the 

 base of insertion of the cylindrical or comb-like " collare setosum." It 

 can hardly be that Ehlers refers to this latter structure by the term 

 "Kragen," since this is merely cuticular. In my opinion the " Dia- 

 phragma" of Nitsche cannot be homologized with the cirri of Endo- 

 procta, because it is merely a part of the body wall comparable to that 

 part from which the " polypide " of Endoproctous Bryozoa arises, and 

 beneath which the tentacles or " cirri " arise. This part of the body w'all 

 is provided with a sphincter in Endoprocta as well as Ectoprocta, and by 

 it the atrial cavity may in both cases be closed. 



