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- 

 tolsemata as taking place in the manner just suggested for Paludicella. 

 His studies were made, he says, preferably on statobkst animals. Nitsche 

 ('75, p. 358) concluded that in Phylactola^mata the x-ing 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 embi-yo 

 which Braem figures. ISTevertheless 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 diflferent 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 YI. Fig. 52, can. crc). 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 appeal's 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, km]), drm. 

 This growth of the lophophoi'ic I'idge naturally does not result in making 

 the tentacles project farther above the ridge. Their elongation must 



