438 
MR. H. N. MOSELEY ON THE STRUCTURE OF THE STYLASTERID2E. 
The gastrozooids are structurally composed of the same number of layers as the 
dactylozooids. The ectoderm forms on these zooids a somewhat thinner layer than 
on the dactylozooids. Definite cell structure was not made out in it. It is, however, 
full of nuclei, and is no doubt definitely cellular in the living condition. It is not, as 
in the case of the dactylozooids, thickly beset with nematocysts, but contains very 
few of these bodies (Plate 43, figs. 1 and 5). 
On the inner surface of the ectoderm in combination with the basement membrane 
occurs a muscular layer which is very highly developed. The layer is composed of a 
series of longitudinally disposed muscular slips, which are set side by side with narrow 
interspaces, so as to form a thick layer (Plate 43, fig. 6). This layer is extremely 
thick and dense towards the base of the zooid, as will be seen from Plate 36, M, and 
becomes gradually thinner and less conspicuous towards the hypostome. The 
muscular slips are stout and closely set towards the base of the zooid, and prominent 
objects in transverse sections of it in that region (Plate 43, fig. 5), whilst they are 
widely separate and fine, and far less numerous towards the upper regions of the 
zooid (Plate 43, fig. 1, M), where little is to be seen but the transparent basement 
membrane. The muscular slips are composed of very distinctly differentiated cells 
which have mostly a fusiform shape (Plate 43, fig. 8), with the tails of the cells 
usually somewhat bent. Many cells are found to occur amongst the mass which are 
apparently in the act of division, two fusiform bodies being connected together by a 
string, or broad mass, of protoplasm. Such cells are so numerous that possibly a 
considerable proportion of the muscular elements remain permanently in this compound 
condition. The cells are closely fitted together side by side to form the muscular slips 
which, where most developed, have a breadth of three or four cells (Plate 43, fig. 7). 
The longitudinal muscular slips pass from the bases of the zooids to spread out 
beneath the ectoderm of the four main canals of the coenosarc, in which the cavities of 
the zooids terminate interiorly. 
Fused with the muscular layer, occurs, as in the dactylozooids, a continuous layer of 
membrane. This basement membrane is transparent, and the only structure which I 
have seen in it is a striation transverse to the longer axes of the zooids, which, as 
already stated in reference to the dactylozooids, I at first believed to give evidence of 
the existence of circular muscular fibres in the zooids. Such fibres I have however 
been unable to discover on closer examination. 
Beneath the membranous layer lies the endoderm. This is composed, towards the 
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 (Plate 43, 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 the uppermost region of the zooid, where the 
direction 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 
