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



upper region of the zooid and in the hypostome, of elongate ovoid cells, with an inflated 

 appearance, very transparent, each containing a small nucleus. These cells, as is well 

 seen in transverse sections (PL X. fig. 1, G), are packed side by side to form the 

 endodermal liuing of the zooid, with their longer axes directed inwards, radially, 

 towards the axis of the zooid, except towards its uppermost region where the direc- 

 tion of these cells is modified by the peculiar rectangular form assumed by the zooid. 

 These elongate cells are closely similar to those occurring in a similar situation in 

 other Hydroids, and there can be little doubt that they are gastric in function. It 

 will be observed that they do not occur in the endoderm of the mouthless dactylozooids. 

 Towards the base of the zooid cavity, these cells become shorter and shorter in length, 

 until in the deepest regions they become mere small globular transparent cells, like those 

 composing the endoderm of the dactylozooids. Towards the base of the zooid they 

 are further overlaid by a layer of the pigmented endoderm cells, which form the 

 endodermal lining of the general ccenosarcal meshwork. The lining of the ccenosarcal 

 canals thus becomes continuous with that of the zooid cavity (PL III.). 



The calcareous style projecting up into the cavity of the zooid has reflected over it 

 from its base a covering of ectoderm, and over that it is protected within the zooid cavity 

 by a layer of ordinary pigmented endodermal cells (PL III. St). 



The tentacles of the alimentary zooid of Sporadopora dichotoma were the only ones 

 amongst those of all the Stylastericke which I was able to observe in the fresh condition, 

 and time did not allow of more than a cursory glance at these even. It sufficed, however, 

 to show that the tentacles are, as in the case of Millepora, knobbed at their tips (PL 

 X. fig. 4), and that their stems display the usual characteristic transverse segmentation 

 of the endoderm. 



The knobs of the tentacles are ovoid in form and are densely beset with nematocysts 

 of the smaller variety. The ectodermal layer of the stems of the tentacles contains few or 

 no nematocysts. 



Gonophores. — Although the soft parts of at least three different colonies of 

 Sporadopora dichotoma were examined, these specimens proved all to be male. In all 

 the specimens gonophores were very abundantly present. They occupy the ampullar 

 chambers in the calcareous ccenosteum already described (PL II. fig. 1, G). The male 

 gonophores are ovoid bodies with their long axes directed at right angles to the surface 

 of the coral. Sometimes only one such body is present in an ampulla, sometimes 

 two or three. The outer extremities of the gonophores are sometimes drawn out into 

 a short tail-like prolongation (PL III. G). The bodies vary considerably in dimensions. 

 Often a gonophore which is fully mature and just ready to discharge its contents at 

 the summit of its ampulla (as seen in PL III. G) has beneath it in the deeper part 

 of the same ampulla an immature gonophore, around which latter the ampulla is less 

 dilated. 



