Gametogenesis of the Gall-Fly, N. lenticularis. 477 
produce males, the others females. An attempt was made, in conclusion, 
to connect these phenomena with what is known of sex-determination in 
other animals. 
‘The material on which the observations here recorded were made was 
collected in March and April, 1910; the methods adopted were essentially 
those described in Part I, the eggs laid by each female being fixed and 
preserved separately at intervals from one to nine hours or more after 
being laid. 
In addition to Petrunkewitsch’s fluid another formula of alcoholic 
_ Sublimate was tried (50 per cent. alcohol with sublimate to saturation + 
6 per cent. acetic acid), but the results obtained were inferior to those 
yielded by Petrunkewitsch’s mixture. Additional experiments were made 
to test the conclusion that the eggs laid by any fly are all male- 
producing or all female-producing; 65 flies were sleeved out in March and 
April on oak-trees which had proved successful in the previous year, and 
16 of these yielded galls early in June. Unfortunately many of the galls 
had been attacked by parasites, greatly reducing the number of flies that 
hatched, so that the results, although not discordant with the last year’s 
experiments, are of little value. The only considerable number obtained 
was 12 females from 19 galls produced by one parent. Mr. H. Scott has 
very kindly examined the external characters and mouth parts of a few 
male-producing and female-producing parthenogenetic females, and finds 
no recognisable differences between them except slight differences in size, 
which are probably accidental. 
Maturation of the Eggs of the Sprung (Parthenogenetic) Generation. 
The part of the previous work which chiefly required completion and 
confirmation was that dealing with the maturation of the spring (partheno- 
genetic) eggs. It was found that in the eggs laid by some females polar 
divisions, or, at a later stage, groups of polar chromosomes, occurred, and, 
in the few cases in which the chromosomes of the segmentation mitoses 
could be counted in such eggs, the number appeared to be 10. In eggs 
laid by other females no polar chromosomes could be found, and these eggs 
showed 20 chromosomes where they could be counted in the segmentation 
division-figures. The number of cases observed was, however, not sufficient 
to substantiate this conclusion with certainty, especially since in some of 
the less well-preserved eggs the chromosomes were clumped together in 
the metaphase of the segmentation divisions, and might show in one part 
of the egg what appeared to be 10 or even fewer large chromosomes, 
VOL, LXXXIIIL—B. 2 N 
