Rickett.—Fertilization in Sphaerocarpos. 243 
some described by Allen ( 1919 ) is suggested by a segment which is much 
longer and thicker than any of the others. 
The two nuclei are usually in contact during this phase. 
In many cases the staining method which best showed the nuclear 
details imparted to the cytoplasm only a very slight coloration, so that no 
details concerning its structure could be made out. In all cases, however, 
in which the cytoplasm was deeply enough stained to be carefully studied, 
certain well-marked changes were taking place in it. These changes are 
therefore assumed to be typical of this phase. The changes in question, as 
has already been indicated, involve the massing of a finer and more homo¬ 
geneous portion of the cytoplasm at opposite ends of the egg nucleus. This 
differentiated material now takes the stain quite readily, but nothing can be 
made out of its structure save that it is practically uniform—apparently 
a mass of fine granules, possibly, in the living state, a colloidal liquid uniform in 
composition throughout its extent. In some cases there are faint indications 
of a reticular structure within these polar caps (Fig. 9). At their boundaries 
they merge into the cytoplasmic reticulum. The peripheral region of the 
cytoplasm is very vacuolate, and its substance is mostly concentrated into 
large and conspicuous ray-like structures, of a fibrillar nature, which radiate 
out from the boundaries of the polar caps. The whole appearance suggests 
very strongly a flowing of certain materials in the cytoplasm towards the 
female nucleus, and their aggregation there in a dense mass. A typical 
case of this process is shown in Fig. 9 ; another, in not quite so advanced 
a stage, in Fig. 12. 
In the later stages the polar caps become more dense and apparently 
even more homogeneous, so that it is no longer possible to discern a reticu¬ 
lar structure in them ; they enlarge so as to surround completely the two 
nuclei and to occupy the larger part of the egg. The boundary of the 
material of the polar caps is now much sharper; outside it the cytoplasm 
is alveolar, the alveoli being fairly regular in shape and uniform in size. The 
condition is illustrated in Fig. 16. An indication of the ray-like structures 
formerly present is still seen in the presence of blunt, more or less conical 
projections from the dense into the alveolar cytoplasm, extending sometimes 
quite to the outer boundary of the cell. 
In three cases the central mass of cytoplasm was replaced by a mass of 
granules, more or less radially arranged, as in those cases in Phase 4 described 
above. 
It is while these changes are going on in the egg that the cells of the 
venter begin to divide, so that the wall becomes composed of two layers of 
cells. This division does not occur at the same time in all the cells, and 
the time at which it begins varies greatly. It might perhaps be expected 
that the beginning of these cell divisions would be correlated with some 
definite stage in the fertilization process. As a matter of fact, in the majority 
