396 Experimental Zoology 
same batch. In any case it is not clear, even if large eggs pro- 
duce fewer males and small eggs more males, whether the result 
is due simply to the size determining the sex, or whether 
the female eggs tend to become larger than the male eggs. 
If analogy has any value in this instance, it seems more 
probable, from the cases of Phylloxera, Dinophilus, and 
Hydatina, that sex may be sometimes predetermined in the 
egg and this determines its size. The question needs, however, 
a reéxamination. 
Ratio of Nucleus to Cytoplasm 
In a recent contribution Richard Hertwig has argued that 
sex is determined by the relation of nuclear size to cell size. He 
bases his argument on a supposed analogy with certain condi- 
tions found in the protozoans, and on some experiments of 
his own and of his pupils on Dinophilus, Daphnia, and Frogs. 
The experiments on Daphnia have been already given. Hert- 
wig thinks that after a succession of parthenogenetic generations 
the nucleus’ in the egg-cell slowly increases —to judge by 
analogy with the protozoa —and this leads toward the pro- 
duction of males. This tendency may be held in check by 
a high temperature, but if the temperature is lowered, males 
appear. The argument is clearly based on a highly hypothetical 
comparison, and lacks direct observation in its support. Issa- 
kowitsch’s experiments seem to show that lack of food and not 
temperature determines the turning point in the life-cycle of 
Daphnia. 
Hertwig’s experiments with frogs are very inconclusive, and 
so far as they go lend little or no support in favor of his view. 
Eggs of Rana esculenta, that had been forced to premature ripen- 
ing, fertilized by a male already at its full sexual ripeness, gave 
the following results. Of 40 individuals that reached the frog 
stage, all were males. There was, however, a high rate of 
mortality, and the results may only mean that all the females 
died. In another experiment some eggs were fertilized at once, 
others after 8 hours. The latter Hertwig thinks must have been 
