394 Experimental Zoology 
Effects of Inbreeding 
It is a widespread belief that deterioration in strength or fer- 
tility or in both follows close inbreeding, and while there is some 
evidence to the contrary in many species, still, in a few, the evi- 
dence that we have at present indicates injurious effects. Such 
weakening influence has been supposed to affect the determina- 
tion of sex. Schultze has carried out a series of experiments 
to test this view by closely inbreeding white mice. His results 
show that while for a limited number of births one or the other 
sex may predominate, yet the general averages show approxi- 
mately an equality. 
Size of the Egg 
In three species belonging to widely different groups it has been 
discovered that the size of the egg is correlated in some way with 
sex. In Phylloxera the large eggs develop without fertilization 
into females, and the small eggs into males. In Hydatina senta 
the same rule holds. In Dinophilus apatris, also, there are large 
and small eggs, both of which are supposed to be fertilized. 
The large eggs produce females and the small ones males. One 
of the most striking instances in which sex seemed to ‘be deter- 
mined by, or connected with, the size of the egg is that of the 
silkworm. Joseph, in 1871, and Mme. Brocadello, in 1896, 
stated that the large eggs became females and the small ones 
males. As the following table shows, the small eggs gave from 
88 to 95 per cent of males and the large eggs 82 to 92 per cent 
of females : — 
BROCADELLO’S TABLE FOR THE SILKWORM MOTH 
Rice ies tr a PER pe piesa 
Vartansi dihhorassan 88 82 
Giallo Perugia 95 92 
Chiacian di Chorassan go 92 
Giallo Pirenei 88 : 92 
Giapponese verde 88 88 
89.8 90.6 
