KOFOID: DEVELOPMENT OF LIMAX. 87 
The section shown in Figure 25 cuts the cells of the animal póle ob- 
liquely, and thus exaggerates their relative size somewhat. In addition 
to the central cavity, there are a number of smaller cavities between tho 
cells of the animal pole. "Their relation to the cell boundaries can in 
every case be readily determined in the sections. The larger cavity 
€ of Figure 24 is between two cells whose facet of contact lies parallel 
to the plane of the section ; the cavity therefore appears to traverse a 
cell, though in reality it does not. In the figure it is in direct continuity 
with eavities which are readily seen to be intercellular. "These latter 
cavities appear lenticular in cross section, but they are themselves elon- 
gated as the cavity æ is. There are, in addition to the intercellular 
cavities just described, two others (vac., Figs. 24 and 25), which seem to 
be intracellular). They are both near the central cavity, though not 
in direct contact with the cell membrane in any direction. They are 
both approximately spherical in form, and neither has the sharp and 
definite outline separating it from the protoplasm of the cell that the 
intercellular spaces just described have. Their form, position, and limits 
thus indicate their intracellular nature. They probably are merely intra- 
cellular vacuoles. Their position is suggestive of their fate. They lie 
very near the central cavity, and it may be that their contents ulti- 
mately find their way into it by osmosis, or less probably by rupture of 
the * cell wall.” 
The fate of the fluid eliminated from the lenticular spaces of the earlier 
stages, and from the intercellular spaces of the later stages, is a difficult 
matter to determine. Direct observation gives negative results, for 
although these cavities in the early stages can be seen to develop and 
disappear, it is impossible to say what becomes of their contents. I have 
never seen any evidence of the extrusion of their contents from the egg, 
but this might escape observation, for the cavities are small and their 
contents are transparent, and it is often difficult to determine the point 
at which the contents even of the large cavity are expelled. 
There are, however, some facts which lend support to the view that 
these lenticular spaces of the early stages, and perhaps also the inter- 
cellular spaces of the later stages, contribute directly to the increase of 
the volume of the central cavity. The nuclear conditions of Figures 
23-25 (Plate III.) show beyond question that this twenty-four-cell stage 
is younger than that of Plate V. Fig. 34, where the larger cleavage 
cavity is shown. It seems reasonable to derive the conditions of the 
m 
older stage from those of the younger. he main diflerence between 
the two stages lies in the increased size of the cleavage cavity and the 
