MATURATION OF UNFERTILISED EGG IN TENTHREDINIDA. 585 
is indicated by the fact that in P. luteolum the two outer 
nuclei (halves of the first polar body) do nearly always come 
together into such close contact that it is often hard to decide 
whether they are one or two. 
It has been pointed out that in C. varus, which yields 
females from unfertilised eggs, the two inner polar nuclei lie 
very close together, although they do not fuse. It is possible 
that in this species the nuclei have a third arrangement with 
respect to the sex which they bear, as in Diagram 3— 
Diacram 3. 
Inner. Outer. 
Ones 
SEY Scene ie oes 
1.e. the converse of Diagram 1, which would lead to the same 
type of behaviour as is found in the male-producinug species. 
It is of considerable interest that in rare cases eggs of N. 
ribesii are found which exhibit the female-producing type 
of development (Diagram 2 above, Pl. 1, fig. 12), and it is 
known that in this species occasional females are reared 
from virgin eggs. It may be supposed, therefore, that in a 
small fraction of the eggs of this species the maturation 
divisions occur in such a way as to cause the nuclei to be 
arranged asin P.luteolum or H. rufa, and that in such 
cases females are produced.! 
The ideas here suggested are of course regarded as merely 
tentative, and cannot be tested until the course of events in 
the fertilised egg is accurately known. If it be found, as 
has been suggested above, that in fertilised eggs of N. ribesii 
no conjugation of pronuclei takes place, but that the egg is 
1 Tf in the bee the two polar nuclei which conjugate are respectively male- 
and female-bearing, and if, as Petrunkewitsch maintains, they give rise to the 
testis, then the spermatozoa of the bee should bear both sexes. But Meves 
(‘Anat. Auzeiger,’ xxiv, 1904, p. 29) has shown that in the spermatogenesis 
of the bee a sort of polar body-formation takes place, and it may be supposed 
that the male-bearing cells are thus eliminated, so that the mature spermatozoa 
would all be female-bearing, as Castle has suggested. 
