No: 24) (-A7IERODE OCTOPUS, GRYELOTALPA, COSTA. 323 
a large, clear nucleus (@) below the outer edge of the ventral 
plate, while in Fig. 47 the protoplasm (f/.) of a cell also at the 
edge of the ventral plate has spread out over the surface of the 
yolk for some distance, anda large stellate cell (¢) is seen beneath 
it. Ido not think that these cells arise by division from the 
ventral plate, as Della Valle ('93) supposes. I draw this con- 
clusion because there is no cell above the one shown in Fig. 
36 from which it could divide, and especially because these 
cells at this stage are very different from those of the ventral 
plate, and their nuclei are similar to those of the dorsal cells. 
It may be that they are analogous to the vitellophags of the 
isopods, which arise from the PD cell, described by Dr. Mc- 
Murrich.‘ The dorsal cells of Microdeutopus and the vitello- 
phags of Jaera resemble each other in three points: in that 
they appear during the segmentation stage, in that their nuclei 
have a characteristic appearance, and in that they are over- 
grown by the ventral plate. The vitellophags in Jaera also 
give rise to mesoderm. The dorsal cells in Microdeutopus, 
however, take no part in the digestion of the yolk. After the 
ventral plate has completely inclosed the egg the dorsal cells 
have lost their characteristic appearance, and they cannot be 
distinguished from the other cells of the second layer. 
I have still to add that, to judge from the appearance of 
embryos like the ones shown in Figs. 29, 32, and 33, the cells 
of the GH group also are overgrown by the descendants of the 
AB and CD groups. 
In the head region of the embryo, in the stages shown in 
Figs. 29 and 33, numerous cells are found in the lower layer,} 
whereas only a few large stellate cells (overgrown dorsal cells) 
are found under the ventral plate in the postnaupliar region. 
At a little later stage (Fig. 30) there are more cells in the lower 
layer of the postnaupliar region than could be accounted for by 
the division of the stellate cells. They are found in patches 
irregularly scattered throughout the region of the ventral plate. 
As I had a very complete series of embryos, I do not believe that 
1 The mesoderm cells are not represented in Figs. 27 and 31, because they were 
so numerous at these stages that they could not be well represented, and because 
the regular arrangement of the ectoderm would have been obscured. 
