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 is not 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 



