68 THE VOYAGE OF H.M.S. CHALLENGER. 



these tubular cavities are set in a circle, at the bottoms of the interspaces between the 

 pseudosepta, at points about equidistant between the inner extremities of the pseudo- 

 septa and the outer margins of the chambers which they enclose (PI. II. fig. 15). 



The ampullar are confined to the zones around the pore systems, and do not occur 

 on the branches. Their cavities are usually kidney-shaped. 



Soft structures of Astylus subviridis. 



The general arrangement of the soft structures is represented on Plate VIII. fig. 1. 



Ccenosarc. — The usual surface layer is present, which is continuous with the sacs of 

 the zooids. A fine superficial reticulation of smaller ccenosarcal canals (PI. VIII. 

 fig. 1, SS) extends over the surfaces of the branches and anipullse, and coral generally, 

 beneath the surface layer. The axes of the branches are occupied by meshworks of 

 large canals, which lead from one cyclo-system to another, and place the whole of the 

 systems in free communication with one another. 



Large canals are given off from the periphery of the gastrozooids. Some of these 

 communicate directly with the axial meshwork of canals, whilst another set passes 

 upwards in the wall of each cyclo-system to join, after a certain small amount of 

 ramification and anastomosis, the basis of the dactylozooid. From the surface of the 

 meshwork of these latter canals which adjoins the dactylopore cavity, a few transverse 

 smaller canals are given 011", which pass inwards radially to be attached to the wall of 

 the pore-sac, and represent the more fully-developed " radial offsets," already described 

 as occurring in Allopora profunda (PI. VIII. fig. 1, R). 



The ampullar sacs are embedded in a meshwork of offsets of the larger canals, and 

 each of the gonophores is attached to one or more stout canal branches. 



Stout offsets of the deeper canal meshwork traverse the interior of the pseudoseptal 

 laminae, and especially near the summits of the pseudosepta large tortuous branches 

 pass radially outwards between the dactylozooid sacs, and, branching at their outer 

 extremities, join the surface network at the margins of the cyclo-sy steins (PL IX. fig. 2). 

 Just over the outer extremities of each of the pseudosepta, at the margin of the top of 

 each cyclo-system, and in the angles between the outer margins of the dactylopores, 

 are situated ovoid nematophores. A single nematophore is placed in each above- 

 described position. The nematophores are ovoid sacs, closely packed with about three 

 tiers of nematocysts of the larger form, placed with their longer axes parallel to those 

 of the containing sacs (PI. IX. fig. 2, N). 



The endoderm of the soft parts in the present form were observed to have, in the 

 fresh condition, a dusky bluish-green colour, with which the whole ccenosarc and 

 zooids of the recent animal when dredged were seen to be tinged. The pigment is 

 soluble in alcohol, and yields a green solution, which produces a well-marked absorption- 



