MATURATION OF UNFERTILISED EGG IN TENTHREDINIDH. 563 
but, when females arise from unfertilised eggs, it seemed 
possible that the fate of the polar bodies would be diiterent, 
as Petrunkewitsch found it in the fertilised eggs of the bee. 
The present paper gives the results of my investigations of 
this matter as far as they have yet gone. 
Before proceeding to describe the maturation of the egg it 
is necessary to give some account of the evidence for the 
statement that virgin eggs of some species produce males, of 
others females. 
In two of the species used there can be no doubt, viz, 
Croesus varus and Poecilosoma luteolum. In the 
first the male is not certainly known, one observer only 
having described it, and all agree that females alone arise 
from virgin eggs. In P. luteolum the male is extremely 
rare, and Miss Chawner, 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 diminu- 
tion in the fertility of the females. <A third species used, 
Hemichroa rufa, is known to give chiefly females from 
virgin eggs, but occasionally males are produced. 
Of the male-producing species I have assumed _ that 
Nematus pavidus yields only males on the authority of 
Cameron’s ‘Monograph of Phytophagous Hymenoptera’ 
(Vol. ii, p. 173), and N. lacteus is so closely related to it 
that it probably belongs to this group, but of this I have no 
certain evidence, since my larve all died off.! The greater 
part of the work was done on N. ribesii (N. ventricosus 
of von Siebold), and in this case the evidence is not quite 
conclusive. It is agreed by all who have bred this species in 
quantity that all, or very nearly all, the flies reared from 
virgin eggs are males. Von Siebold (11, p. 121) obtained 
thirteen ¢ ? among about 1700 ¢ ¢ from virgin eggs, and 
supposes that these were introduced with the food. Other 
observers have obtained only males. It is always possible, 
however, that the females die off as larve; that they do not 
1 Miss Chawner writes to me that she has reared males only from virgin 
eggs of N. lacteus. 
