MATURATION OF UNFERTILISED EGG IN TENTHREDINID®. 583 
quent fusion with the second was found in some unfertilised 
eggs of Lasius niger, and in both fertilised and virgin 
eges of Bombyx mori. 
It is evident, therefore, that the fate of the polar nuclei 
may differ very considerably in different insects. The case 
which one would expect to be most closely parallel] with the 
sawflies is that of Rhodites rose, for this species is not 
only placed near them in classification, but is also partheno- 
genetic. In several points Henking’s description is similar 
to that which I have given, the peculiar arrangement of the 
chromatin in the egg-nucleus at the beginning of the first 
polar mitosis is very like what I have observed in N. ribesii, 
and both forms seem to be peculiar in having no true reduc- 
tion division, both the polar mitoses being probably equational. 
But Rhodites differs in two important points; according to 
Henking there is a doubling of the chromosome number at 
the first division of the egg-nucleus, which he supposes is 
bronght about by the separation of chromosomes which have 
paired before the first polar mitosis; and there is at least a 
partial fusion between the inner polar nuclei, all of which in 
this case remain as groups of chromosomes, and do not 
develop a nuclear membrane. Among the sawflies investi- 
gated, with the possible exception of C. varus and a few 
abnormal eggs of P. luteolum, a tendency to fusion of these 
nuclei was observed only in male-producing species, and 
Rhodites produces females from virgin eggs. Since conju- 
gation of the two inner polar nuclei takes place also in the fer- 
tilised eges of the bee and of N. ribesii, which yield females, 
and apparently quite irregularly in other insects, it must be 
concluded that it alone can supply no evidence as to the 
causes which determine sex; but when all the facts which I 
have given are considered together, it seems to me that some 
indication is offered of the direction in which the solution of 
the problem may be sought. 
Castle (1) has suggested that the second maturation 
division may consist in the separation of a male-bearing from 
a female-bearing nucleus. And Le Dantee has propounded 
