126 THE VOYAGE OF H.M.S. CHALLENGEB. 



Development of Alcyonarians and Zoantharians compared. — It seems extremely 

 difficult to reconcile the extraordinary succession of the mesenteries in the development 

 of the Zoantharians, discovered by Lacaze-Duthiers, with the facts presented by Alcyona- 

 rians. Did the development of the eight mesenteries of Alcyonaria correspond with that 

 of the first eight mesenteries formed in Actiniada?, the first mesenteries formed would be 

 either the lateral dorsal or lateral ventral ; but these are those which are most rudimen- 

 tary in the zooids of Sarcophyton. Moreover, the mesenterial filaments of the two lateral 

 pairs of septa are in the development of Actiniadte the first to appear, and not the dorsal, 

 which are longest in the Alcyonarian polyps and most persistent in the zooids. 



Apparently, however, development in Alcyonarians follows a different course. 

 In Halysceptrum, the development of which has been examined by Kolliker, the 

 eight mesenteries appear from the very first. In Kalliphobe (Busch), one of the 

 Edwardsise, according to Metschnikoff, the larva has, in its earliest stage, eight tentacles 

 and two mesenterial filaments. 



