MUSEUM OF COMPARATIVE ZOÖLOGY. 108 
resent roughly a phylogenetic stage ancestral to both groups of Bryozoa, 
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 lead to the Ectoproct stage: first, 
the closure of the tentacular corona posteriorly in front of the anus (Plate 
V. Fig. 43), and, secondly, the formation of the 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 Nitsche 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 (76, p. 
132) utterances concerning the lack of homology 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 wall 
is provided with a sphincter in Endoprocta as well as Ectoprocta, and by 
it the atrial cavity may in both cases be closed. 
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