2 Edmund B. Wilson 



Kophohelemnon and FunicuUna. In Alcyonium and Paralcyonium^ the 

 dorsal filaments make their appearance at about the sanie tinie with 

 the others (see fig. 3) . Very soon, however, the dorsal filaments out- 

 strip the others in development , so that when the bud is not more than 

 half grown they may be several times as long- as the latter (see fig. 4). 

 In Gorgonia the filaments all appear at aboiit the same time , so far as 

 I could determine, and the dorsal pair become after a time longer than 

 the others, though much less so than in Alcyonium. 



In the development of these organs we have therefore a simple bnt 

 rather striking case of eontrast between the sexual and asexual repro- 

 duction of an animai, and the structure of the polyps is simple enough 

 to warrant the hope that it may be possible to discover the cause of 

 this eontrast. For this reason I have studied at Naples the structure 

 and development of the mesenterial filaments in several genera oi Alcyo- 

 naria^ and the novelty of the results has been unexpected. The result 

 of this study has been firstly, as I believe, to show clearly the cause 

 of the difference between the egg-development and the bud-develop- 

 ment where this exists ; secondly , to demonstrate that among the so- 

 called mesenterial filaments of the Akyoìiaria we have to distinguish 

 two kinds of organs which difiPer fundamentally in structure, develop- 

 ment, and function ; and thirdly, to suggest certain comparisons between 

 the Anthozoa and the Enterocoela which so far as I know have not 

 hitherto been considered, and which involve an entirely new conception 

 of the morphology of a polyp. 



It has been noticed by nearly all observers of the Alcyotiaria that 

 the dorsal pair of filaments are iuvariably longer and narrower than the 

 other six. It was observed also that they have a different structure from 

 the others, though this difference has never been carefully investigated ; 

 indeed the mesenterial filaments in general have been little studied, many 

 observers contenting themselves with the somewhat vague statement 

 that »the filaments have the usuai structure«. Nevertheless . the dorsal 

 filaments have always been supposed to be of entodermic origin like 

 the others — that is, simple thickenings ' of the edges of the dorsal 

 septa, which are purely entodermic structures. I have however found 

 that while this is strictly true of the six shovter filaments , the dorsal 

 pair are, on the contrary, entirely of ectodermic origin, 

 being unmistakably downgrowths from the invaginated 

 ectoderm of the Oesophagus. This curious fact, which I suspected 

 but did not succeed in proving in the case of Renilla^ shows that the 

 dorsal filaments are morphologically quite different structures from the 



