446 
MR. H. N. MOSELEY ON THE STRUCTURE OF THE STYLASTERIM. 
the contracted condition clavate in form. The base of the zooid rests on the style of 
the containing gastropore, which in the retracted condition of the zooid appears to 
project into the gastric cavity to a considerable distance as in Sporcidopora. The 
ectodermal covering of the gastrozooids is composed of transparent ovoid cells 
(Plate 44, fig. 4), which form a layer resting upon a substratum containing numerous 
nuclei and bounded by the basement membrane. The gastric endodermal lining of 
the zooids is composed of elongate cells of closely similar nature to those occurring in 
Sporcidopora. The mouth appears, when closed, as a crucial slit ; four main canals 
usually lead from the base of the zooid cavity to the coenosarcal mesliwork. 
Fresh zooids are added to the colony by means of buds arising from the surface layer 
of the coenosarc at points where this is joined by offsets of the superficial canals of 
the coenosarcal mesliwork. Such a bud is represented in Plate 37, D. The part 
of the superficial layer immediately surrounding the bud is depressed and forms the 
sac of the zooid. 
Gonopliores. — Only female examples of Errina labiata were obtained for examination. 
The female gonophores are closely similar in structure to those already described as 
occurring in Pliobothrus symmetricus ; but there is this great difference — that whilst in 
Pliobotlirus the ampullae and their contained ova and planulae remain until maturity 
immersed in the corallum beneath its surface, in Errina the ampullae project more and 
more above the surface as development proceeds. 
The spadix in Errina labiata is at first cup-shaped (Plate 37, S), the walls of the cup 
being composed of a very thick layer of endodenn. The cavity of the cup is directed 
towards the surface of the coral, and within it rests the large single ovum with its 
distinct germinal vesicle and spot. Each ampulla contains invariably only one spadix 
and ovum. The ovum is covered over in the cup by a reflection of the ectodermal 
investment of the spadix (Plate 44, fig. 4). 
The stages of yelk division were not detected. The ovum becomes developed into 
the condition of a planula within the ampulla. As development proceeds, the embryo 
becomes gradually greatly increased in size, and assumes a form corresponding to that 
of the containing ampulla already described. As the process proceeds, the spadix 
becomes divided at its margin into a series of lobes, which lobes sub-divide, branch 
and unite to form a network, and encroach over the surface of the embryo until more 
than half of- the proximal surface of the embryo becomes thus embraced by the 
reticulate cup of the spadix (Plate 37, S'). 
The ectodermal layer of the embryo seems to be formed from the general mass by 
delamination. No trace of any process of invagination was observed; but all stages 
were seen which would appear to prove that the ectoderm layer is gradually differ- 
entiated at the surface from the outer elements of the mass. The ectodermal layer 
when first observable as distinct, appears finely granular in structure, whilst the 
abundant endodermal mass is composed in large part of highly refracting oil-globules. 
Hie ectoderm, as development proceeds, shows a striation directed perpendicularly 
