354 SYDNEY J. HICKSON. 



A.lcyonia or Lobularife^ taking A. di git at urn for the type, in 

 the outer surface being covered with a continuous crustaceous 

 coat, and in each of the polyps being enclosed in a distinct 

 tubular sheath projecting from the general surface. It differs 

 from all the Alcyonia in the polyps being only half retractile." 

 I have examined a couple of specimens sent to me from the 

 Marine Biological Association's laboratory at Plymouth, and I 

 am able to give a figure of the spicules (fig. 5). The descriptions 

 given by both Couch and Gray are fairly accurate, but, as I 

 shall point out presently, the condition of retraction of the 

 polyps is not a character upon which too much reliance can 

 be placed for purposes of classification, as it is one which 

 depends so largely upon the means employed to kill and pre- 

 serve the colony. 



A. glomeratum (Hassall), then, differs from A. digitatum 

 (Linn.), in that the lobes are more pointed and more deeply 

 divided, the spicules are reddish in colour, and there are no 

 dumb-bell-shaped spicules. 



Section III. — General Anatomy. 



The colony of Alcyonium digitatum is composed of a 

 number of polyps which are fused together for the greater part 

 of their length, but have each a free extensible and retractile 

 portion which bears the mouth and tentacles. The mesogloea 

 of the larger portion of the body-wall of each polyp is con- 

 siderably thickened, and in direct connection with that of its 

 neighbours, so that no limits can be drawn in this region 

 between one polyp and another. 



In most of the text-books of zoology it is customary to 

 restrict the term '' polyp " to the free extensible portions of 

 the individuals, and to give the name "coenosarc" to the part 

 of the colony which is composed of their fused basal portions. 

 It cannot be too strongly insisted upon that this is an erroneous 

 conception of the structure of Alcyonium. The dorsal mesen- 

 terial filaments of each primary polyp extend to the base of 

 the colony, the ventral mesenteries are visible as ridge-like 



