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



of these specialised zooids along a branch is always the same, and may be indicated in 

 the following manner, using the letter E to indicate gonozooid and S the gastrozooid: — 



R— S— R— R— S— R— &c. (cf. PL VIII. fig. 3). 



The fission by which the dimorphism is probably produced alters the relation of each 

 zooid to its axis. In both gastrozooid and gonozooid the sagittal axis is longer than the 

 transverse, so that now the long axis of each zooid is at right angles to the axis of the 

 branch instead of being parallel with it. There is no difference in shape between the two 

 types, but the gastrozooid can always be distinguished by the presence of an oral opening 

 in the centre of the peristome ; this is usually situated at the summit of a conical or 

 cylindrical projection (PI. VIII. fig. 3). 



Each zooid bears two tentacles, both of which are of the same type, usually fusiform 

 and of considerable length. In specimens in which the ova are well developed the 

 gonozooids become much distended, and are then usually different in colour from the 

 gastrozooids. In Schizopathes crassa the gonozooids have a distinct yellow tint, whilst 

 the gastrozooids are a dirty white in spirit preparations. Nearly all the species referred 

 to this subfamily have been obtained at great depths. 



Schizopathes. 



In this genus the zooids are closely packed, like a number of beads arranged 

 along one surface of the axis. In side view there is scarcely any interval between 

 the individual zooids in normal portions of the colony, and adjoining gonozooids are 1 as 

 close together as each gonozooid is to the gastrozooid to which it morphologically belongs. 



In the gastrozooid the mouth is situated at the apex of a cylindrical projection 

 of the peristome, which is of considerable length in Schizopathes crassa. A series of 

 horizontal sections shows that there is no marked elongation of the stomoda3um in the 

 sagittal axis, usually such an elongation does not exist at all. The ectodermal lining is 

 thrown into dendritic folds, and a lumen is rarely visible in the upper portion of the 

 stomodajum. Ten mesenteries are present in the gastrozooid, all of which are of similar- 

 breadth in the upper sections of the oral cylinder. These, as in Antipathinae, are divisible 

 into six primary and four secondary mesenteries ; the arrangement is the same as in 

 Antipathcs and other allied genera. Towards the base of the oral cylinder the secondary 

 mesenteries become lost, apparently remaining attached to the wall of the cylinder after 

 having lost their connection with the stomodseuni. The secondary mesenteries in Schizo- 

 pathes crassa all disappear before the plane is reached at which the two tentacles become 

 continuous with the general surface of the peristome. At this point the stomodseum is 

 somewhat elongated in the transverse direction, and the transverse mesenteries being- 

 broader than the others the whole oral cylinder is, at its base, oval in outline, its long 

 axis corresponding with that of the branch. Still lower down, where the lumen of each 



