PROCESS OF FERTILIZATION IN THE CRAB 135 
course of development. The first evident step in the transfor- 
mation of the spermatid is the appearance of vacuoles in the 
cytoplasm next to the nucleus. These are small at first but by 
coalescing they soon form a large, clear vacuole on one side of 
the nucleus (figs. 33 to 38). Sometimes it appears that the 
vacuole may have arisen by the nucleus settling to one side of 
the clear space surrounding it as in figure 31. The nuclei, each 
with its accompanying vacuole, now lie in a common mass of 
cytoplasm. In the further development of these cells there are 
three parts which must be constantly borne in mind, namely, 
the nucleus, the vacuole (hereafter called the capsule) and the 
cytoplasm. We will take up certain stages in the differentiation 
of these three parts, and consider their relation to each other. 
In figures 37 to 41 the shape of the nucleus may be some- 
what modified by strains in the cytoplasm or by the crowding 
of the elements in the tubule. In these drawings there is no 
evidence of a granular or reticular structure, although such struc- 
ture was made out in some preparations which were destained 
to a greater degree. In figure 37 it may be observed that the 
outer layer of the nucleus stains more densely than the inner 
portion. The nucleus in figure 38 contains a vacuole which does 
not take the stain. The cytoplasm surrounding the nucleus and 
capsule in figures 37 to 39 is nearly uniform in appearance, with 
probably a tendency to be a little more deeply stained near the 
nucleus. In figures 40 and 41 there is a concentration of a por- 
tion of the cytoplasm on one side of the capsule and bordering 
the nucleus. ‘This is finely alveolar and stains more deeply than 
the rest of the cytoplasm. It may be that this patch of cyto- 
plasm is seen in an earlier stage in figure 36c, a. This portion 
of the cytoplasm crowds in between the nucleus and the capsule 
(fig. 42). About this time the capsule begins to take a brownish 
color when stained with iron-hematoxylin. 
The origin and development of this portion of cytoplasm which 
appears on the side of the capsule and nucleus and wedges in 
between them is a striking feature in the development of the 
spermatozoon. Its behavior is well brought out in figures 45 to 
48. In figure 45 we see this substance slipped in like a wedge 
