22 BULLETIN OF THE 
(occasionally dividing) representing the blind end of the pocket and 
lying between the inner and outer layers, both of which are intact. 
Braem (’90, p. 50) describes the formation of the ring canal in Phylac- 
tolemata as taking place in the manner just suggested for Paludicella. 
His studies were made, he says, preferably on statoblast animals. Nitsche 
(75, p. 358) concluded that in Phylactolemata the ring canal was first 
a furrow, whose lips fused, and my own study (’90, p. 129) has led me to 
the same conclusion. Since reading Braem’s account I have looked over 
some of my own sections of Cristatella again. Certainly the process is 
not so clear in the buds of the adult colony as in the statoblast embryo 
which Braem figures. Nevertheless the series of sections (90, Plate IV. 
Figs. 33-38) given as evidence of my statement still seem to me capable 
only of the conclusion I drew from them. Perhaps the processes may 
be different in detail in the two cases; certainly the two explanations 
are not fundamentally dissimilar. 
The ring canal being established in the oral part of the polypide, it 
grows forward, as I have said, and, secondarily, the canals of both 
sides meet in the median oral line and their lumina become confluent 
(Plate VI. Fig. 52, can. erc.). From what has already been said, it is 
clear that the lateral parts of the ring canal are not now continuous 
with each other behind. They become so only after the formation of 
the tentacles. 
The tentacles arise upon the lophophoric ridge at a stage a little later 
than that represented in Plate IV. Figure 32. At the stage represented 
by Figure 35, however, the tentacles have begun to form, as indicated by 
the fact that in the series from which this figure was taken the fold into 
the upper part of the atrium appears now deep, now shallow, according 
as the section passes through the length. of a young tentacle, or only 
through the lophophoric ridge between the tentacles. The position of 
the section (Fig. 35) is about the middle of the series, corresponding 
to Figure 32. 
By a comparison of Figure 35 with Figure 32 in respect to the tenta- 
cles, it will be apparent, first of all, that the lophophoric ridge itself has 
been heightened and that this heightening has been effected, not by a 
deepening of the fold existing in Figure 32, the lips of the fold remain- 
ing quiescent, but by a movement downwards of the outer lip (*) of the 
groove which is to form the ring canal. The movement is of course ac- 
companied by an increase in the length of the kamptoderm, kmp. drm. 
This growth of the lophophoric ridge naturally does not result in making 
the tentacles project farther above the ridge. Their elongation must 
