92 



meets the body-wall at two circular lines of contact, thus dividin<,'^ the coelom into the: unpaired 

 proboscis-cavity and the two pairs of cavities characteristic of the adult. The external division 

 of the bud into the three regions has meanwhile been ]jrogressing. The future metasome is 

 directly continuous with the young stalk, and its body-cavities are hence prolongations of those 

 ot the parent stalk. The intestinal limb of the alimentary canal develops as a dorsal diverticulum 

 of the originally simple enteric sac, and fig. 39 of the original memoir shews it passing from 

 its origin freely through the body-cavity, the coelomic epithelium dipping down between it and 

 the stomach. The intestine grows dorsally till it meets the body-wall, when it opens to the 

 exterior by the anus, which is from the first in its definitive position. The pharyngeal region 

 gives rise to evaginations which form liic notochord and the gill-slits. The ovaries are developed 

 from the wall of the coelom ; but the oviducts, like the collar-pores, are ectodermic invaginations. 

 The arms are of course formed as donsal outgrowths of the collar. 



Fowler (04), in describing the budding of Rhabdopleura^ states that most of the alimentary 

 canal is probably derived from a thin-walled tube present in the mesentery of the parent-stalk, 

 and he supposes that this tube is of endodermic origin. The commencement of the alimentary 

 canal is, however, believed to be formed from ectoderm, and it is from this stomodaeal portion 

 that he believes the notochord to origfinate. 



The analogy of the Tunicata shews that there is no a priori improbability in Fowlkr's 

 account of the origin of the alimentary canal; antl the supposed endodermic tube of the stalk 

 could be regarded as an epicardium-Iike formation. I'rom such observations as 1 have been able 

 to make on the budding, I am, however, inclined t<j think that Mastkrmax is right in deriving 

 the entire alimentary canal of the bud from ectoderm, a process which is believed by the majority 

 of investigators to take place in the budding of the Ectoproct Polyzoa. I have, moreover, given 

 reasons above (p. 78) for believing that the "endodermic" tube in the stalk of Rhabdoplejira 

 is the posterior stalk-vessel. Fowler has not, as a matter of fact, brought forward evidence 

 shewing that this structure gives rise to an)- part oi the alimentary canal of the bud; and, on 

 the analogy of Cephalodiscus, I consider it probable that the entire alimentary canal of Rhabdo- 

 pleura is derived from a single "Anlage". If this be the case, 1''owler's contention that the 

 notochord of Rhabdopleura is morphologically ectodermic loses most of its force, since it might 

 be argued on similar grounds that the entire alimentary canal of Cep ha Iodise us is to be regarded 

 as a stomodaeum. 



It may be noted that Mastkr.max's account of the origin of the coelomic cavities of the 

 bud is similar to that which has been given by Scmultz (03, i) of the origin of the cavities 

 in regenerating specimens of Phoronis, in which both the preseptal and the postseptal cavities 

 are derived from the general body-cavity. 



There appears to be a marked contrast between C. dodecalophus and C. levinscni on 

 the one hand, and C. gracilis and C. sibogac on the other hantl, in respect of the extent to 

 which the blastozooids remain connected with one another. It may, however, be remarked of 

 C. levinseni that the colony a])pears to have been killed at a season when budding was not 

 taking place with special activity. 



C. gracilis and C. sibogae on the contrary shew a distinct tendency to the production 



