500 ROBERT W. HEGNER 
and are recognizable as oocytes (fig. 6, 0). This is brought about 
by an increase in the amount of cytoplasm and by the enlarge- 
ment of the nucleus. The arrangement of the chromatin within 
the nucleus changes during this differentiation; that of the nurse 
cells (fig. 6, n) retains the condition characteristic of the rosette 
stage (fig. 2), whereas in the newly formed oocytes the chromatin 
forms threads which are scattered about irregularly within the 
nucleus (fig. 6, 0). The connecting strands, so noticeable in the 
rosettes (fig. 3), either disappear at this time or lose their stain- 
ing capacity since they are apparently absent from this stage on. 
Nevertheless it is very easy to determine which cells have de- 
scended from a single mother cell since a dark double ring re- 
mains where the strands passed from one cell to another (fig. 7). 
These rings are quite conspicuous but were completely over- 
looked by Paulcke (’01). 
The change from the rosette zone to the zone of differentenaen 
_in the ovariole of the bee is an abrupt one—a fact which makes 
a study of the differentiation of the oocyte difficult, since no 
intermediate stages can be studied unless material in just the 
proper condition is obtained. In several cases which will be 
described later, investigators have found that a single rosette 
gives rise to one oocyte and a group of nurse cells. This is cer- 
tainly not true in the bee, since the oocytes in the zone of differ- 
entiation are much too numerous, compared with the number of 
rosettes, and many instances were observed of two or ‘more 
oocytes which had been directly connected by. spindle remains 
as indicated by the presence of double rings between them (fig. 7). 
If all of the cells in a single rosette are potentially alike the 
question arises, what causes some of the cells to become oocytes 
and others nurse cells? Three explanations have occurred to 
me: (1) There may be differential changes during the mitotic 
divisions in rosette formation as in Dytiscus (Giardina ’01) 
resulting in one or more cells (oocytes) which differ in content 
from the others (nurse cells). No Visible changes of this sort 
were observed. (2) The polarity of the rosette may influence 
the cells in such a way that those near the center of the ovariole 
and closest to the zone of differentiation tend to develop into 
