576 L. DONCASTER. 
polar mitosis, and shows two polar nuclei, and the remains 
of the third nearer to the edge of the egg; the egg-nucleus 
has already sunk into the yolk, and is not seen in the same 
section (Pl. 36, fig. 22). ‘The two inner nuclei lie very near 
together in the polar protoplasm, which is very small, often 
being visible in only one section. Rather later, a small 
compact group of chromosomes is found, which at this stage 
appear always to be seven or eight in number (fig. 23 a). 
Since I have not been able to find the maturation mitoses, I 
cannot say certainly that these chromosomes are derived 
from one nucleus, but analogy with the other species makes 
it highly probable that this is the case. The stage here 
described is reached probably about two hours after the egg 
is laid, and in eggs preserved an hour or two later a group 
of about fourteen to sixteen chromosomes is found in the 
polar protoplasm (fig. 23b). It seems, therefore, that as in 
N. ribesii the chromosomes of the polar nucleus may split, 
but remain aggregated together in one group. Beyond this 
stage I have not been able to trace them. 
C. varus seems to occupy a position intermediate between 
N. lacteus and Hemichroa rufa (described below); it 
resembles N. lacteus in apparently showing incipient con- 
jugation of the two inner polar nuclei, but, as in H. rufa, 
only one of these seems to break up into chromosomes, while 
the other disappears completely. 
8. HEMICHROA RUFA. 
In this species, according to Cameron, unfertilised eggs 
yield both males and females, but females are much more 
abundant. The eggs are embedded in rows in the larger 
ribs of alder leaves, each egg lying in a separate incision 
and being completely covered by the leaf-tissue. In this 
case also it was necessary to let the flies lay on branches 
enclosed in muslin. 
The earliest stage found is the second polar mitosis, in 
which, as in other species, two spindles lie in a line perpen- 
