OOGENESIS IN PHILOSAMIA 15 
Dytiscidae a markedly regular division of tetrads, each part 
giving rise to a whole tetrad, this process being repeated several 
times. In P. cynthia there is no evidence of any order in the 
fragmentation, for there is the greatest irregularity in the size 
and shape of the pieces. 
The period of fragmentation marks the first broad phase in 
the history of the nurse cells. It is interesting to note that 
the cells have passed through a cycle of changes as if for matura- 
tion divisions, since they show the reduced number of chromo- 
somes. These are destined, however, only for disintegration. 
Stages 7 to l. At the beginning of this phase, the eggs and 
nurse cells are practically similar in size (fig. 37 e). The egg 
cell increases steadily in size during the growth period. the 
nurse cells, although increasing for a time, do not keep pace 
with the growth of the egg, and become relatively smaller as 
development proceeds. 
Stage 7 (figs. 37 e and 53): At the close of fragmentation, 
numerous small dark granules lie within the nucleus near the 
periphery, together with a variable number of larger round 
bodies, which, although stained very deeply in some sections, 
are very pale in others, and appear to be of the nature of plasmo- 
somes. The cell contents appear slightly granular, or reticular, 
with a very darkly granular, flask-shaped area extending from 
the nuclei toward one end of the cell, appearing to perforate 
the cell wall in the form of a curved tube which enters the egg 
cell. Marshall (’07), Giinthert (’10) and others describe similar 
areas, but the tubular portion is not apparent. A later stage is 
shown in figure 54. The nuclear wall is less easily seen on the 
side nearest the tubes, for the granules are thickest at this point, 
and lie close to the dark granular cytoplasm. In addition to 
this mass of granules, the nucleus contains much smaller masses 
scattered near the periphery, and several small plasmosomes. 
A thin dark band of cytoplasm often encircles the nucleus, merg- 
ing with the flask-shaped portion. Beyond this the cytoplasm 
appears reticular. Figure 55 A shows another cell in which 
the nuclear cavity is indented in two regions, giving a somewhat 
dumb-bell shape. During these changes in the shape of the 
