BUA}; | T. H. Morgan 
According to Cameron, Nematus pavidus gives rise only to 
males from virgin eggs, and Miss Chawber™ has reared males 
only from virgin eggs of Nematus lacteus. 
Von Siebold found only 13 females among 1700 males from the 
virgin eggs of Nematus ribesii. Doncaster finds that many virgin 
eggs do not develop, the percentage being lower than that for 
fertilized eggs. 
The fact that virgin eggs in several species of saw-flies produce 
males and females, or either males or females proves conclusively 
that the egg of these hymenoptera may produce both or either sex. 
This result seems to me to indicate with some probability that in 
general the eggs in this group have the double possibility and that 
some mechanism exists by means of which the virgin egg is thrown, 
as it were, in one or the other direction towards the female side in 
Peecilosoma luteolum, towards the male side in other members of 
the group and in the bee. What turns the balance in these cases 
is still unknown, but it is evident that a closer scrutiny of the polar 
body formation and the events that immediately follow is needed. 
In the “gall-flies” (Cynpidz) there are several species known in 
which two generations alternate. One generation is composed 
exclusively of females that lay parthenogenetic eggs from which 
males and females hatch. Here once more we find eggs which 
without being fertilized produce both sexes. In the generation 
composed of males and females the fertilized eggs—presumably all 
are fertilized —produce only females that are parthenogenetic as 
we have just seen. 
THE INFLUENCE OF THE ENVIRONMENT ON PARTHENOGENETIC 
REPRODUCTION 
It is in connection with parthenogenesis that the results here 
recorded for phylloxera and aphids have particular interest, for it 
is in the parthenogenetic egg that sex is determined. [In two other 
groups of animals the relation between sex and parthenogenesis is 
so similar to that in phylloxerans and aphids that comparisons 
must inevitably be made. 
18 See Doncaster, footnote, p. 563. 
