224 MURIEL ROBERTSON. 
cess of sphere formation occurs both in the colony and in the 
free condition. ‘These spheres are destined to give rise to the 
gametes. 
Development of the Spheres.—In tracing out the de- 
velopment of the spheres it is more convenient to consider 
first the case of a single-sphered individual and thereafter to 
note the slight differences that occur in the cases where there 
are more than one sphere. The sphere arises directly from 
the nucleus (cf. figs. 13-19). In the very earliest stage the 
nucleus differs only from the resting nucleus in that the rays 
have become thicker and the membrane more distinct (fig. 
13a). Later the whole nucleus increases in size and the 
karyosome assumes a somewhat eccentric position. The first 
signs of the sphere itself now beginto appear. The substance 
within the nucleus becomes differentiated—showing a different 
staining reaction, e. g. blue with Romanowski—to form aspheri- 
cal mass which fills almost the whole nuclear space. The rays 
now appear as small rounded masses ; some of these are within 
the sphere ; the greater number, however, lie on the outside and 
seem rather to be connected with the membrane which at this 
stage appears surrounding the sphere with its enclosed karyo- 
some (fig. 13) than with the sphere itself. The karyosome 
gradually moves further from the centre until it finally comes 
to lie quite outside the sphere (fig. 14h). It appears to take 
no further part in the process. The position of the karyosome 
at any one moment bears no exact relation to the size of the 
sphere. It is sometimes to be seen lying within a compara- 
tively large sphere, in other cases it is already on the outside 
although the sphere occupies little more than the space of 
the original nucleus. The size of the sphere has, however, no 
very constant relation to its state of development. 
In the stage shown in fig. 14 the small chromatin masses 
derived from the rays have decreased in number. ‘Those on 
the outside have as a rule disappeared, though in some cases 
they can just be distinguished as very minute particles. 
Those inside the sphere now appear as definite spherical 
masses ; in one case I could only count three of these. 
