DR. E. B. WILSON ON THE DEVELOPMENT OF RENILLA. vol 
small rounded granular bodies, about one-fourth the size of the yolk-cells and destitute 
of nuclei ; and fifth, still smaller granules, apparently produced by the disintegration 
of the preceding. 
The entoderm (en.) has now a very different appearance from that of the last stage. 
The cells are columnar, with very distinct oval nuclei, which are always situated in the 
outer half of the cells; but the cell-contents are dark and opaque, being densely 
packed with granules. The cell-outlines are thus more or less obscured, and though 
always distinct towards the outer part of the cell may be quite invisible towards the 
base. The granulation is of quite different appearance in the inner and outer parts of 
the cells. In the basal (7.¢., outer) part the granules are fine and closely packed, and 
are left nearly or quite unstained, while in the inner ends of the cells the granulation 
is coarse and irregular, and stains more readily, This difference is so constant that in 
most specimens the basal granulation forms a pretty distinct narrow zone extending 
around the entire entoderm. ‘The cells are in some parts of the sections only one 
layer deep, but in other parts the entoderm consists of several layers and varies greatly 
in thickness. 
The general features of a twenty-nine-hours’ larva are shown in fig. 128, and a por- 
tion of the body-wall, more highly magnified, in fig. 129. The body is now distinctly 
elongated and the oral end can be distinguished by its greater size. The entoderm is 
composed of high columnar cells, and is everywhere much thicker than the ectoderm. 
The gastric cavity is clearly defined and the yolk-mass is greatly reduced in bulk. 
Under a high power (fig. 129) the yolk-cells are found to have nearly disappeared, 
though here and there one may still be recognised. The yolk is almost entirely com- 
posed of the naked granular spheroidal bodies described in the last stage. They vary 
a good deal in size, but are on the average rather larger than the nuclei of the entoderm 
cells. They appear to have had their origin in the breaking up of the yolk-cells, 
though some of them are perhaps small yolk-cells which have lost their nuclei. 
The entoderm cells (e.) are much elongated and present some interesting characters. 
Towards their bases they are filled as before with fine granules, which stain very 
slightly, and are arranged in a distinct zone encircling the entire larva. Their inner 
portions (apical) present a confused coarsely granular appearance, entirely unlike that 
of the basal granulation. The cells seem to contain rounded granular masses, which 
have the same appearance as the smalier spheroidal bodies of the yolk, which le 
outside the cells in the stomach cavity. As in the last stage, the granules are so 
abundant that it is difficult to make out the outlines of the cells, which only appear 
clear and well defined at their inner ends. 
The yolk gradually disappears as development progresses and the larva rapidly 
increases in size. Much variation exists in the length of time required for absorption, 
but it is always complete, so far as I have observed, by the forty-eighth hour, and the 
gastric cavity is left empty, or sometimes containing a small quantity of a delicate 
débris, which appears to be the remains of the membranes of the yolk-cells. After 
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