98 



I fully admit that the evidence afforded by the stages which have so far been described 

 is anything but convincing with regard to certain points, but in the next stage figured (figs. 

 178 — 180) we are on surer ground. The sections are in much the same plane as the preceding 

 ones, and are from a bud in which the first pair of arms is beginning to develop. 



In fig. 178 are seen the proboscis and collar with their respective cavities, the collar- 

 cavity being prolonged into the developing arm (a./.). A portion of the metasome {met.), with 

 its body-cavity, is cut tangentially. 



In fig. 179, the proboscis and collar are cut medianly. The proboscis has not only become 

 somewhat flattened, but it shews another of its adult characters in having a ventral lobe composed 

 of a fold of ectoderm, with ba.sement-membrane between the two layers, but not containing a 

 prolongation of the proboscis-cavity. The pericardium {per.) possesses a thickening on its posterior 

 wall which indicates the wall of the future vascular space. The mouth {m.) and part of the 

 alimentary canal are well developed, although the posterior outline of the latter is obscurely 

 marked off from the epithelium of the third body-cavit\-. The notochord {nch.) is present, beyond 

 doubt, as a small diverticulum of the pharynx, reaching the wall of the pericardium. 



In fig. 180, the middle line has been passed, so that the other collar-cavity and first 

 arm are cut, while the coelomic sac of the proboscis is cut tangentially. The bud was probably 

 not lying with its axis in one plane, since the trunk is cut oblicjuely transversely to its main 

 axis. The intestinal limb of the alimentary canal, which meets tlie body-wall in the position of 

 the future anus, is connected with the ventral wall of the body by the median mesentery, on 

 either side of which are the paired third body-cavities. 



Assuming that the pericardium here described is M.\sterm.\x's "subneural sinus", it will 

 be noticed that this specimen lends no support to the statement of that author (98, 2, p. 516, 

 figs. 37, 39) that the notochord (= "subneural gland") is at first at some distance from the 

 pericardium (= "subneural sinus") and at a later stage .shifts its position so as to meet it. 



I think that there is very little reason to believe that the structure marked sti.g. by 

 M.\STERM.\x in fig. 37 has anything to do with the "subneural gland", a structure which I 

 describe under the name of notochord. In stages so late as his figs. 37 and 39 I should not 

 have expected to see a body-cavity extending continuously from the proboscis to the metasome 

 on the ventral side of the pericardium; and for this reason and for others which I have explained 

 above I cannot consider the figures in question as anything but diagrams (probably combination- 

 figures), representing M.\sterm.\n's views with regard to the structure of the buds. 



The five body-cavities and the pericardium are easily recognisable from the stage represented 

 in figs. 178 — 180 onwards, the third body-cavities remaining continuous with those of the parent- 

 stalk until the bud is liberated, e.xcept so far as they are obliterated in the stalk of the bud 

 by the development of muscles and connective tissue. The early appearance of the pericardium 

 as a sliarply marked epithelial sac is certainly one of the most characteristic features of the 

 budding of C. dodccalophus. 



The bilateral origin of the buds is well shewn in figs. 169 and 172. 



The parent slalk is turned forwards towards the jjroboscis, and its terminal sucker is cut 



