590 J. BRONTE OATEN BY. 
nection, if any, with the mitochondria or Nebenkern, is 
unknown to me. 
The Differentiation of an Indifferent Germinal 
Epithelial Cell into a Nurse or Yolk Cell. 
It is quite usual to find small yolk granules in any indifferent 
epithelial cell, and when the cell becomes either an oogonium 
or a spermatogonium, these soon disappear at first (see PI. 30, 
fig. 6). The growth of an indifferent cell into a yolk cell is 
accompanied by the appearance of abundant yolk disclets, and 
a change in the size and in the disposition of the chromatin of 
the nucleus. In the latter the chromatin bridges between the 
angular lumps if present (PL 30, fig. 2) become lost and the 
chromatin becomes formed into little round structures. Syn- 
chronously with the appearance of more and more yolk, the 
nucleus grows larger and larger till it may be 35 jj. in length. 
These changes are easily noticed and have already been 
described well (2). A more difficult problem is what happens 
to the plasmatic bodies of the modified cell. Does a Nebenkern 
appear ? What happens to the mitochondria ? It is not at 
all easy to find answers to these questions. In PI. 33, fig. 38, 
is drawn a cell with a yolk cell nucleus gathered into 
numerous chromatin lumps. In the cytoplasm there were no 
yolk disclets, but the reticulum was of the very wide kind, 
peculiar to yolk cells. Here and there were small masses 
containing mitochondria (. M .), and to the left of the nucleus 
was what I took to be an attraction sphere, inside which were 
embedded a number of dark bodies, probably the Nebenkern. 
In many ways this cell is intermediate between the yolk 
cell and the indifferent epithelial cell. In the full yolk 
cell it is probably not possible to discover attraction sphere, 
Nebenkern, or mitochondria. But after many of the yolk 
discs have been absorbed by neighbouring cells, it is generally 
possible to discover bodies shaped like those drawn in the 
oocyte in PI. 31, fig. 12, at X.N.K. What these are, subse- 
quent work will be needed to show, but I liave done enough 
