The meßenterial Filaments of the Alcyonaria. 19 



Leioptilum Virgularia 



Sarcophyllum Acanthoptilum 



Renilla 

 Witli the single partial exception oi Stylohelemnoti , in whieh some of 

 the zooids are said to open directly into the sexual polyps, thezooids 

 of list A communicate at their bases with the feeding 

 polyps only through the finer canal-system. 



We will examine separately the zooids of list B. 



The case of Pteroides is very important since both forms of zooids 

 coexist in the same colony. Those of the »Zooidplatte«, which alone 

 possess filaments, open into a spongy network ofcanals. All of the 

 other zooids open either directly into the feeding polyps, 

 or bymeansof a short canal, directly into the m ai n longi- 

 tudinal canal s. This is obviously a strong confirmation of my hypo- 

 thesis. The zooids of Virgularia are stated to open either directly into 

 the polyps, or in some cases into the canal-system. The anatomical 

 relations of AcantJioptihmi are not described, and the case of Renilla I 

 have already considered. The zooids of Leioptilum and Sarcophyllum 

 possess no filaments and nevertheless open into the canal-system. This 

 case I am unable to explain as it Stands. 



Upon the whole, I think, these facts lend support to my hypothe- 

 sis, as to the office of the filaments in the zooids ; and the case of Pter- 

 oides teils strongly in its favor. It may perhaps be justifiable to expect 

 that the two adverse cases may in future be explained by the discovery 

 of special conditious which cannot be perceived from Kölliker's brief 

 and general descriptions. 



Lastly we may consider the significance of the position of the ciliat- 

 ed bands. It is a strikiug fact that in Alcyonarian colonies the dorsal 

 radial Chamber appears to be always turned in a definite direction. In 

 the penniform Pennaitdida it seems to be always turned forwards — i. e. 

 towards the tip of the colony. In compact colonies, \ike Sarcophyton, He- 

 liopora^j Älcyonium^ Paralcyonium^ the dorsal Chamber is turned towards 

 the axis of the colony in the »polyp-cell« and hence upwards in the free 

 part of the polyp. The same is true of Veretillum which forms a compact 

 mass like an Alcyonium brauch . The foregoing considerations enable us 

 to understand why the ectodermic bands should be placed upon the dorsal 

 septa. If we examine a brauch oi Alcyonium (fig. 15) we observe that the 

 young buds, />. , always arise in the angle between two older buds 



' MoSELEY, Phil. Trans. Vol. 166, Parti, p. 121. 



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