AND DEVELOPMENT OF MYRIOTHELA. 
559 
composing it contain only clear colourless protoplasm, with some clear granules ; but 
towards the distal pole of the gonophore the cells increase slightly in size, and contain 
purple granules, which form a coloured ring internal and parallel to that belonging to 
the outer layer (figs. 7 & 10, a). In the centre of this internal ring the layer now under 
consideration is perforated by a narrow aperture, which thus lies immediately under the 
distal pole of the gonophore, which is itself quite imperforate. 
The last described layer encloses the mass of the generative elements (figs. 7, 10, & 12), 
from which, however, it is separated by a very thin structureless membrane (fig. 12, e), 
by which the whole generative mass is surrounded, and which becomes reflected over 
the spadix where this is plunged into the midst of the mass of ova or spermatozoa. 
DEVELOPMENT. 
The first appearance of the gonophore shows itself in a minute offset of the gastric 
cavity of the blastostyle. This pushes itself outwards into the ectoderm of the blastostyle, 
carrying with it the endoderm, which continues to form its immediate boundary, sepa- 
rated from the cellular ectoderm by the hyaline lamella ; but no well-defined external 
projection has yet become apparent. 
The endoderm (Plate 57. fig. 1, a), which lies over the distal end of this gastric diver- 
ticulum, soon becomes excavated by a cavity of a nearly spherical shape ( b ). This 
cavity, which I shall speak of as the gonogenetic chamber, is separated from that of the 
diverticulum ( c ) by a considerable thickness of the endodermal layer ; but the endoderm, 
which bounds it distally, forms a cellular membrane of only a single cell in thickness. 
The cavity, which as yet appears quite closed, is filled with clear contents, in which no 
formed matter beyond minute granules can be detected. 
In the next stage the diverticulum from the Cavity of the blastostyle has increased in 
size, and continuing to press the endoderm and ectoderm before it, the whole has 
begun to form a well-defined hernial projection from the side of the blastostyle, while 
the floor of the gonogenetic chamber has become convex ; and the chamber, which has 
at the same time increased in size, presents in longitudinal section a crescentic shape. 
A minute orifice has now become visible in the summit of the chamber ; and the endo- 
dermal cells, which immediately surround the orifice, have become somewhat larger, 
and are seen to be filled with brown pigment granules. The ectoderm continues imper- 
forate, the orifice being entirely confined to the thin layer of endoderm which forms the 
immediate roof of the gonogenetic chamber. 
Up to this point there is nothing by which the male and female gonophores may be 
distinguished from one another. We soon, however, observe a differentiation of the con- 
tents of the gonogenetic chamber. In the female gonophore a layer of more consistent 
protoplasm has accumulated on the free surface of the walls of this chamber (fig. 2, b), 
more especially on its proximal wall or floor. Minute, clear, nucleus-like bodies may 
be seen scattered through the protoplasm, and a few similar bodies float free in the more 
liquid contents which still occupy the centre of the chamber. 
4 e 2 
