348 Experimental Zoology 
may be produced either on the eggs in the ovary or on the eggs 
after they are laid, or on the embryo itself. Another experiment 
described below is required to settle this question. The main 
point at present is that the sex changes with the temperature. 
Nussbaum has objected to this conclusion on the grounds that 
it isnot clear whether Maupas’s calculations rest only on the rela- 
tive sizes of the eggs produced, or on the kind of individuals that 
emerged. If on the former, the result must be inconclusive be- 
cause many eggs of intermediate size are usually present that 
cannot be accurately referred to one rather than to the other 
sex. It is improbable, I think, that Maupas has made such a 
mistake. Nussbaum also points out that at 26° to 28° C. the con- 
ditions were not favorable, as shown by the relatively small num- 
ber (104) of eggs produced. The maximum number for this many 
individuals would be 250 eggs. The results may, therefore, 
have been due to insufficient nourishment rather than to tem- 
perature. 
In another similar experiment Maupas got the same results. 
Thus, five young Hydratina females laid their first eggs at a 
temperature of 14° to 28° C. Twenty-four per cent of these 
eggs produced individuals that laid male eggs, and 76 per cent 
produced individuals that laid female eggs. Five other indi- 
viduals were kept at a higher temperature, 26° to 28° C., and laid 
118 eggs, of which 81 per cent gave rise to individuals that pro- 
duced male eggs and only 19 per cent produced individuals that 
laid female eggs. 
Maupas found that under different conditions of temperature 
the same individual may at one time produce eggs that give rise 
to females that lay only female eggs, and at another time may 
produce eggs that give rise to individuals that lay only male eggs. 
The result shows that whether the egg becomes a male-producing 
or a female-producing individual is determined after it has been 
laid and not while it is in the ovary. Nussbaum’s results show, 
in fact, that this is determined during the course of the first few 
hours after the individual hatches. 
Maupas isolated six young females. They were kept in the 
