THE DEVELOPMENT OF THE OAPE CEPHALODI8CU8. 195 
of the undivided egg’, but still comparatively few (about ten 
out of several hundreds examined). This probably indicates 
that this stage is passed through at a comparatively rapid 
rate. Segmentation was in all cases total and usually about 
•equal. A typical case is shown in PI. 13, fig. 3, in which the 
blastomeres are about equal. Cases of decidedly unequal 
division, however, occurred as shown in PI. 13, fig. 4, and in 
one case the smaller blastomere was *21 x *16 mm., the 
larger *29 x ’37 mm. A large nucleus with nucleolus was 
conspicuous in some cases in each segment. 
Stages of four blastomeres were about as numerous as 
those of two. In some the second division was of the typical 
form, equal and at right angles to the first (PL 13, fig. 5). 
In others there were decided departures from this type. 
Thus a stage was found (PI. 13, fig. 6), in which the blasto- 
meres did not lie in one plane, each of them being so placed 
that it was in contact with the other three, as if a relative 
change in position had taken place subsequently to the second 
division, or the division spindles of the second division had 
been at right angles to each other. A second aberrant type 
(PI. 13, fig. 7) was found in two cases, in which two segments 
were widely separated, the other two being in close contact 
with each other. Both of these types may be connected with 
the fact, shown in another case, in which the division in one 
segment has been more rapid than in the other, resulting in 
the formation of three blastomeres, one large and two small 
(PI. 13, fig. 8). 
This segmentation may therefore be unequal, not only in 
quantity, but in point of time and method of division, 
probably connected with the great amount of yolk in the egg, 
a fact which also, as will be seen later, has a striking effect 
in further development. It apparently indicates a very inde- 
terminate type of segmentation which is seen also in the next 
stage observed. This consisted of six cells (PL 13, fig- 9)- 
Blastula. 
The earliest appearance of the segmentation cavity was at 
VOL. 62, PART 2. NEW SERIES. 14 
