1911.] Gametogenesis of the Gall-Fly, N. lenticularis. 483 
segmentation stages the nuclei become differentiated into two kinds; some 
will form the blastoderm and continue to divide normally by mitosis, others 
remain as yolk-nuclei and show signs of degeneration in the frequent massing 
together of their chromatin into a single, large, deeply-staining mass, in their 
great variation in size, possibly due to fusion of nuclei in some cases, and 
lastly, in dividing irregularly by amitosis. I find that such “ yolk-nuclei” 
exist also in the blastoderm stages of the summer (fertilised) eggs, and these 
show signs of degeneration and indications of amitosis similar to those found 
in the spring eggs. In an embryo of the summer generation fixed when 
three days old, the yolk is already largely absorbed and the yolk-nuclei 
appear to be undergoing atrophy. Whether these suggestions are correct 
can only be determined by further work on fresh material collected for the 
purpose. 
Ovarian Mitoses of Parthenogenetic Females. 
In the spermatocyte divisions of the male, I described (Part I, pp. 92, 94, 
and 95) a small extra-nuclear body which does not divide with the cell, and 
is, therefore, present in only half the spermatids. It seemed not impossible 
that the presence of this body in half the spermatozoa might determine 
whether the fertilised egg developed into a male-producing or female- 
producing parthenogenetic individual. To recognise such a body in the 
fully grown egg would be almost impossible, owing to the quantity of yolk, 
but 1t seemed just possible that it might occur in the oogonial mitoses of 
some of the parthenogenetic females. I have cut sections of the ovaries of 
seven larvee of the parthenogenetic generation, in the hope of finding it, and 
in five of them oogonial mitoses occur in which no such body is visible. In 
the other two no oogonia are in course of division. It is possible, of course, 
that all these larvae would have developed into female-producing individuals, 
but since the extra-nuclear body is not recognisable in the spermatogonia 
in the male larva, it is more likely that if such a body is present in the 
female at all it is not to be found at so early a stage. 
Mitoses in the Nervous System. 
In a footnote added to the first part of this paper while in proof (Part I, 
p. 91) I mentioned that in the developing nervous system of male larve 
mitoses occurred with the haploid number (10) of chromosomes. Examples 
of this are shown in figs. 26, 27, 28,a; I have not much to add to my earlier 
account. I have found undoubted haploid figures in the nervous system of 
six male larve, and in no male examined are there certainly no such 
mitoses ; in a few, no countable mitoses could be found. In addition to the 
haploid mitoses I have occasionally found diploid figures (figs. 28,0; 29); and 
