316 WHEELER. (Vor. IIL. 
as this path is travelled over when the egg is much smaller, 
and the distance from the centre to the periphery much 
less than in the mature egg. The nucleus of the sperma- 
tozoon entering the egg at some point on the ventral surface 
between s and c, probably at or near #, advances through 
the egg as the male pronucleus z and fuses with the female 
pronucleus, coming from the opposite direction, at a point 
near & The segmentation nucleus passes on -to the point 
/ and divides in the direction of the anteroposterior axis of 
the egg, giving rise to the daughter nuclei wm. By sub- 
sequent divisions these give rise to the blastema nuclei, which 
migrate to the ventral and ventrolateral surfaces of the egg (7). 
It is by a tangential division of the blastema cells, forming a 
layer of much smaller cells, which creep around the sides of 
the egg and close on the dorsal surface, that the blastoderm is 
completed. 
DoRYPHORA. 
Turning now to Doryphora, we find that the ovariole differs 
from that of A/attfa in one particular: The terminal thread di- 
lates below into a large oval chamber (-udkammer), the mem- 
branous wall of which is closely packed with cells of various 
sizes, containing nuclei which vary in size as the inclosing 
cytoplasm varies in volume. The nuclei contain delicate, much 
convoluted chromatin filaments. Besides the difference in size, 
no other differences are perceptible between the different 
cells. 
At the lower end of the Exdkammer the differentiation of 
the cells into ova and follicular epithelium takes place. Careful 
examination of many sections has convinced me that none of 
the peculiar phenomena described by Will (51) in the oogenesis 
of Wepa are to be observed in Doryphora. What I have seen 
is in perfect accord with Leydig’s observations (29). The large 
cells of the Exdkammer become the ova, and the smaller cells, 
after undergoing a further reduction in size by division, become 
the follicular epithelium. 
In the two upper follicles the ova resemble in every respect the 
large cells of the terminal chamber, the nuclei retaining exactly 
the same perfectly spherical form, and the same distribution of 
their chromatin. In the ovum of the third follicle the chromatin 
