2(54 CEYLON PEARL OYSTER REPORT. 



form a tube, usually one cell in thickness, which is at first blocked by a plug of 

 mesogbeal-like substance (pi.). Rudiments of mesenteries frequently appear (m.), 

 and by the removal of the plug an aperture is formed to the exterior. If a bud is 

 destined to become an autozooid, mesenteries appear at a very early stage and 

 usually attain a considerable size before the completion of the stomodseum or 

 formation of the tentacles. My study of the development of the buds is yet incom- 

 plete, but there can be no doubt of the ectodermal origin of the stomodaeum and the 

 endodermal origin of the mesenteries. I have not yet worked out the origin of the 

 ventral mesenterial filaments. 



Canal Systems. 



The canal systems of the Alcyonaria have been described by Hickson (1895) for 

 Alcyonium, Moseley (1881) for Sarcophytum, Ashworth (1898) for Xenia, and 

 Pratt (1903) for Lobophytum and Sclerophytum. 



The canals in Alcyonium are very similar to each other in form and structure, but 

 very irregular in their course ; there appear to be no large vessels which maintain a 

 course parallel to the periphery or to the longitudinal direction of the zooids, so that 

 it is impossible to divide the canals into superficial and internal systems as in 

 Sclerophytum. The vessels of the canal system are most numerous near the surface in 

 the deeper portions of the colony they are very sparingly distributed and are confined 

 to the basal portions of the secondary polyps and the adjacent portions of their 

 neighbours (Hickson, 1895, p. 362, Plate 37, fig. 8). 



In Sclerophytum the superficial and internal canal systems are extremely well 

 marked throughout the colony ; near the base the internal system is very complex, 

 owing to the branching and anastomosing of numerous vessels. In the presence of 

 two systems of canals, and in their manner of distribution, Sclerophytum resembles 

 Xenia. 



The canal system of Sarcophytum is very similar to that of Lobophytum, and 

 differs from Sclerophytum and Xenia in the absence of a superficial system, and 

 in the fact that the principal longitudinal vessels are direct prolongations of the 

 ccelentera of the siphonozooids. 



New canals frequently arise as outgrowths from pre-existing vessels in the follow- 

 ing manner : One or more endoderm cells wander from a canal into the mesoglcea 

 and divide and multiply to form a strand of cells ; the individual cells of the strand 

 multiply and form a fairly solid cord of endoderm, which usually remains attached to 

 the canal from which it grew. Eventually a longitudinal splitting occurs and the 

 lumen of the canal is formed (fig. 23). 



This investigation of the Ceylon Alcyoniidas has been carried out in the Zoological 

 Laboratories of the Victoria University of Manchester. I am greatly indebted to 

 Professor Hickson for much valuable advice and kind assistance in my work. 



