THE DEVELOPMENT OE ALCVONIUM DIGITATUM. 
63 
karyokinetic figures, one daughter nucleus passing to each of 
the eight lobes (PI. 3, fig. 10). After the first segmentation 
the blastomeres may be uniform or may fall into groups of 
four large and four small cells (Text-fig. 30), or again may 
be quite irregular in size. The nucleus in each segment now- 
halves, exhibiting meanwhile well-formed spindles, some with 
equatorial chromosomes and others with the halved chromo- 
somes at each pole. Then the eight cells divide into sixteen, 
generally eight smaller at one pole and eight larger at the 
other. All the blastomeres do not divide simultaneously, and 
hence stages are found with ten, twelve, or fourteen cells 
only, but an examination of the nuclei shows that the undivided 
cells will also shortly segment, giving the typical sixteen cell 
stage. In some fourteen-celled embryos the nuclei of many 
of the segments had again halved ready for the thirty-two 
celled stage before the two slowest of the original eight cells 
had completed their first division. When sixteen lobes are 
protruded the egg divides immediately into sixteen cells 
instead of eight (PI. 3, fig. 11, and Text-fig. 31). These 
segments again may be equal or unequal, and are, as in the 
case of the eight cell stage, separated by a segmentation 
cavity containing a little waste protoplasm. In all cases the 
sixteen cells halve, giving thirty-two blastomeres, and here 
again some segments divide very slowly, and so twenty, 
twenty-four, and twenty-eight celled embryos occur. The 
thirty-two blastomeres (Text-fig. 32) may or may not be 
uniform, and the irregularity in all the previously mentioned 
stages prepares one for and helps to explain other embryos 
where the segmentation seems quite irregular, or where 
numerous very small cells form a cap at one pole over a few 
large cells at the other (Text-fig. 33). Possibly the large 
amount of yolk in the ovum causes the unequal segmentation 
as well as the initial futile attempts at division and the 
retardation of fission in some blastomeres. The thirty-two 
celled embryo divides repeatedly, giving sixty-four, one 
hundred and twenty-eight, etc., cells. By this time the 
embryo has become two-layered, the segments at each division 
