THE DEVELOPMENT OF PEKIPATUS CAPENSIS. 457 
which closely adjoins the dark patches of the three other cells 
at the animal pole, and which contains a central clear area 
(fig. 5). 
The two first furrows, therefore, are at right angles to one 
another, and in the vertical plane. The next furrow is hori- 
zontal, and divides each of the four segments into two unequal 
parts ; a small animal part consisting almost if not entirely of 
the dark animal part of the cell, and a larger, clearer mass ; so 
that the ovum now consists of eight cells, four small cells lying 
close together at the animal pole, and consisting almost entirely 
of the darkly granular parts of the cells of the previous stage, 
and four large, clearer, but more or less granular cells. Each 
of the small dark cells contains a central transparent area, which 
I take, as before stated, to be the expression of the nucleus. 
The four small dark cells give rise to the ectoderm, 
and the four larger cells to the endoderm. — The sub- 
sequent division of these two kinds of cells proceeds inde- 
pendently. 
In the next stage I have figured (fig. 7), there are eight dark 
cells, each with its central clear area, and an undetermined 
number of large endoderm cells. 
At the end of segmentation (fig. 8), the ovum consists of a 
number of large-branched endoderm cells scattered irregu- 
larly within the egg membrane, while the ectoderm cells con- 
sist of a mosaic of more or less hexagonal cells closely applied 
together and placed close to the membrane on one side at 
about the middle of the long axis of the egg. 
The egg at this stage presents a very peculiar appearance, 
and I would not believe for some time that I was not dealing 
with an abnormal or injured ovum. But I found the stage so 
often, and so many stages intermediate between it and the 
earlier and later stages of development, that I cannot but believe 
in its normal existence. I found it also when every precaution 
was taken to avoid injuring the ovum ; when I merely opened 
the animal and examined the ovum through the transparent 
walls of the oviduct without even touching any part of the 
female organs. 
