POLYZOA. . 301 



The first distinct rudiment of the polype appears as a white 

 body, which gradually develops into the alimentary canal and 

 lophophore. While this is developing the ectocyst grows rapidly 

 larger, and the yolk in its interior separates from the walls "and 

 occupies a position in the body cavity of the future polype, 

 usually behind the developing alimentary canal. According 

 to Nitsche (No. 316) it is attached to a protoplasmic cord 

 (funiculus) which connects the fundus of the stomach with the 

 wall of the cell. It is probably (Nitsche, etc.) simply employed 

 as nutritive material, but, according to Barrois, becomes con- 

 verted into the muscles, especially the retractor muscles. 



Adopting the hypothesis already suggested in the case of the 

 Entoprocta the metamorphosis just described would seem to be 

 a case of budding accompanied by the destruction of the original 

 larva. 



This view of the nature of the post-embryonic metamorphosis is appa- 

 rently that of Claparede and Salensky, and is supported by Claparede's 

 statement that the formation of the first polype ' resembles to a hair ' that of 

 the subsequent buds. The mode of budding would, however, appear to 

 present certain peculiarities, in that the whole larval skin passes directly into 

 the bud, while from the rudimentary bud of the larva the lophophore and 

 alimentary tract only of the fixed polype are formed. 



Flustrella and Cyphonautes. The next group of larval 

 forms is that of which Cyphonautes is the best known type. 

 The larvae composing it at first sight appear to have but little in 

 common with the larvae hitherto described. The researches 

 of Barrois (No. 298) and Metschnikoff (No. 314), (but especially 

 those of the former on the early stages of Flustrella hispida, the 

 larva of which is very similar in form to Cyphonautes, though 

 without so great a complexity of organisation), have given a 

 satisfactory basis for a general comparison of Cyphonautes with 

 other ectoproctous larvae. 



The segmentation and early stages of the embryo of Flus- 

 trella resemble closely those of Alcyonidium. A projecting ring 

 of large cells is formed, dividing the larva into oral and aboral 

 parts. The oral part soon however becomes very small as com- 

 pared with the aboral, and becomes vertically flattened so as to be 

 nearly on a level with the ring of large cells. In the next stage 

 the flattening becomes completed ; and the ring of large cells 



