FROM THE INDIAN AND PACIFIC OCEANS. 



21 



of growth and the mode of branching of the canal-system. Siphonogorgia is a solid 

 massive growth in which both stem and branches are round and cylindrical, the whole 

 colony being of a rigid brittle consistency. Chironephthya may or may not have a round 

 cylindrical stem, but the branches lose the solid appearance and become somewhat flattened 

 and deeply grooved, and the terminal twigs are very much more slender than those of 

 Siphonogorgia. Turning now to a section, the reason for this becomes obvious. In the 

 barren stem of Siphonogorgia (text-fig. 1) there is one large central canal and numerous 



Fig. 1. 



Fix. 2. 



Fig. 1. — Transverse section through the barren stem of Siphonogorgia rotunda. In this and the succeeding text- 

 figures the mesoglcea is represented in black ; the cavities occupied by the spicules before decalcification 

 are left white; the endoderm lining the central canal and solenia is represented conventionally. 



Fig. 2. — A transverse section through the stem of Chironephthya pendula. 



small anastomosing solenia ; the whole ccenenchyma is studded witli numerous spicules of 

 varying size with their long axes vertical, to the presence of which the stem owes its 

 rigidity. In the branches (text-fig. 3) the main canal will have divided into several 

 secondary branches, which in their turn branch further until they terminate in a polyp- 

 cavity. The solenia of the branches are few in number ; quantities of spicules are again 

 found everywhere. 



In the stem of Chironephthya (text-fig. 2) there is a ring of about eight canals 

 surrounding amass of coenenchyme practically without spicules; outside this rirg the 

 coenenchyme is filled with spicules, but their absence from the centre makes the stem 

 very much more lax than that of Siphonogorgia. In the branches (text-fig. 4) the canals 

 become immense and the coenenchyme is very much reduced, and in consequence of there 

 being no solid mass of tissue strengthened with spicules to keep the branch stiff and 

 rigid the walls collapse and give the grooved irregular effect already noticed. 



In this family, as Professor Hickson (i8)has already pointed out, a study of the 

 spicule arrangement in the polyps is disappointing, for no single colony or even branch 

 of a colony has exactly similar polyps, but the extent of the variation is not very great ; 

 in fact, a general type of arrangement can be given as a diagnostic character of the 



