3G2 SYDNEY J. HTCKSON. 



The mesenterial filaments may be seen through the trans- 

 parent body-wall of a fully expanded living polyp. The single 

 pair of dorsal filaments may be readily distinguished from the 

 other six by proceeding in almost straight lines from the edge 

 of the stomodaeum down into the depths of the coelenteron ; 

 and if they be traced further in sections of preserved speci- 

 mens, they may be seen to continue right down to the base of 

 the polyp, — that is to say, in the case of the primary polyps to 

 the base of the colony^ and in the case of the secondary polyps 

 to that part of the endodermal canal system from which they, 

 as buds, arose (PL 37, fig. 6). 



The four lateral and two ventral mesenterial filaments are very 

 short, and even in the most fully expanded polyps present a very 

 sinuous outline. It is difficult to say what their exact length is, 

 as I have found it impossible to measure them accurately in 

 the living polyp ; but judging from the length of the tentacles, 

 and other measurements that I have obtained accurately, I 

 should say that they are never more than 2 — 2*5 mm. long. 



The gonads are spherical bodies, reaching in their mature 

 condition a diametrical measurement of about 0"5 mm. When 

 ripe the ova are of an orange-red colour, the sperm-sacs milky 

 white. They are covered by a coat of endoderm continuous 

 with the endoderm of the lateral and ventral mesenteries, to 

 which they are attached by short stalks. They are invariably 

 attached either to the side or edge of the free portion of the 

 mesenteries below the termination of the mesenterial filaments, 

 and never extend for a distance of more than 10 mm. 



The gonads do not occur, so far as my observations go, on 

 the dorsal pair of mesenteries. 



As stated above, the coelentera of the diflPerent polyps com- 

 posing the Alcyonium colony do not communicate with one 

 another directly, but running in the mesoglcea between the 

 cavities there are canals, lined by endoderm, with a wide 

 lumen, by means of which the water can flow from the ccelen- 

 teron of one polyp into that of its neighbours. In the peri- 

 pheral portions these canals are fairly numerous, but they are 

 very scanty in the deeper parts of the colony, being almost 



