Sex Determination in Phylloxerans and Aphids 313 
wasp and ant. It is true that two polar bodies are given off from 
all eggs as in the bee, according to Doncaster, but he describes two 
types of eggs, those in which reduction occurs and those in which 
it does not occur. His suggestion that only those eggs are capable 
of fertilization in which reduction occurs may appear to account for 
the sexual eggs, but it still leaves unexplained how two polar bodies 
can be extruded from the egg that produces a male without a reduc- 
tion of the chromosomes. 
In an earlier paper Doncaster called attention to certain facts, 
that appear to be well established, showing that in the saw-flies (Ten- 
thredinidz) virgin eggs produce males in some species, females in 
others. In Croesus varus “the male is not certainly known, one 
observer only having described it, and all agree that females alone 
arise from virgin eggs.”’ [t should be recalled in this connection 
that Doncaster finds two polar bodies given off from this egg. He 
is driven to assume, in consequence, that both divisions are equa- 
tional, but this is obviously an argument ad hoc and out of har- 
mony with the general trend of modern cytology. His observation, 
that two of the three polar bodies fuse, might be brought into har- 
mony with the similar observation made by Petrunkewitch, and if, 
as the latter believes, the fused product makes the reproductive 
organ, the germ cells would then have the double number of chro- 
mosomes and reduction be possible in the egg. But there is 
serious doubt in regard to Petrunkewitsch’s conclusion and Sil- 
vestri’s observations on certain Chalcidz show, in fact, that the 
polar bodies take no part in the development of the reproductive 
organs of these hymenoptera; yet the facts of development are 
identical with those in the bee. There is obviously something that 
is still lacking in these observations on the saw-flies, that makes it 
impossible to harmonize the results with the facts in other forms. 
Doncaster points out that in Poecilosoma luteolum the male is 
extremely rare, “and Miss Chawber of Lyndhurst tells me that 
she has bred thousands of this species for several years in succession 
without obtaining a male and without finding any diminution in the 
fertility of the females.”’ 
Hemichroa rufa produces “chiefly females from virgin eggs but 
occasionally males are produced.” 
c 
