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 lining 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. II.). 
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. II. St). 
The tentacles of the alimentary zooid of Sporadopora dichotoma were the only ones 
amongst those of all the Stylasteridee 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 sufticed, however, 
to show that the tentacles are, as in the case of Millepora, knobbed at their tips (PI. 
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. IL. 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. HI. G) has beneath it in the deeper part 
of the same ampulla an immature gonophore, around which latter the ampulla is less 
dilated. 
