736 DR. E. B. WILSON ON THE DEVELOPMENT OF RENILLA. 
The egg shown in figs. 73 to 106 developed nearly in the manner just described, 
but with the important difference that the delamination cleavage appeared to take 
place when the embryo consisted of thirty-two (+) imstead of sixteen spheres. 
When first observed the egg consisted of thirty-two (+) spheres (fig. 73), which 
afterwards flattened together very completely (fig. 74). Fifteen minutes later the 
spheres swelled up and became very prominent (fig. 75), but the embryo passed into 
another quiescent stage (fig. 76) without visible division of the spheres. 
Hence it would seem that the period at which delamination occurs is not invariable, 
or it may be that it takes place at different periods in different parts of the same egg. 
The number of eggs observed was not large enough to determine this interesting and 
important point. 
The remainder of the segmentation (figs. 77 to 85) is closely similar to Renilla 
and does not call for special remark. . The periods of activity and quiescence alternate 
with great regularity, and have approximately the same duration as in Renilla. 
Although I have examined a considerable number of eggs (probably fifty or sixty), 
they were never found to consist of less than sixteen spheres or undergoing “partial” 
segmentation ; and although some inequality was observed, this was never so marked 
as in Renilla. It would therefore seem that the form of segmentation is more firmly 
fixed than in Renilla. 
$2. Internal phenomena of segmentation. 
a. The unsegmented egg. 
In the fresh state no trace of a germinal vesicle can be seen in the unsegmented 
egg. A series of sections shows, however, that a large vesicle is present (fig. 86) 
containing a very distinct germinal spot. In immature eggs the vesicle lies near the 
centre of the egg, but in the ripe egg it is situated near the periphery of the vitellus. 
It is enclosed in a delicate but very distinct membrane, and has a somewhat reniform 
shape with the concave side turned outwards. The interior appears to be filled with a 
finely granular substance, which stains intensely. No protoplasmic reticulum can be 
seen, and if present its meshes must be of exceeding fineness so as to produce the 
appearance of a fine granulation. The germinal spot is of a rounded form and lies 
near the centre of the germinal vesicle. It is of high refrangibility and stains 
intensely with picro-carmine. Under a high magnifying power it is seen to consist of 
a lighter clear peripheral layer, enclosing a number of spheroidal bodies, which are 
separated by a reticulum of deeply staining substance. 
The body of the vitellus consists of a fine protoplasmic network, closely packed 
with rounded granules of deutoplasm, which are scarcely affected by the staining fluid. 
A rather narrow peripheral zone of the vitellus does not take the staining fluid, and is 
of a more finely granular structure than the rest of the vitellus. This zone is faintly 
visible in fresh eggs when flattened under the compressor, and it persists until a late 
