Life-cycle of the Rotifer; Hydatina Senta 349 
cold and laid there 34 eggs, of which 12 per cent only became 
individuals that laid male eggs and 88 per cent individuals that 
laid female eggs. The same parents were then transferred to 
a warmer temperature and laid 95 eggs that were male pro- 
ducersand 5 eggs that were female producers. They were changed 
back and forth from warmth to cold, and each time a correspond- 
ing change occurred in the individual that came from the eggs. 
During the last four days of their life they produced 50 eggs, 
of which 17 per cent were male-producing and 83 per cent 
female-producing. 
Nussbaum has tried to show that the sex of the offspring is de- 
termined by the environment and not by influences on the egg. 
If the young parthenogenetic female after she has emerged is 
well fed, she produces large eggs that develop, without fertiliza- 
tion, into female individuals. If on the other hand an individual 
is at first poorly fed, she produces small eggs, and these develop 
without fertilization into males. Before and after this period 
the sex of the egg is not determined by the food supply, 7.e. after 
the first egg has been laid it is no longer possible to change the 
sex of the other eggs. 
Nussbaum thinks that Maupas was mistaken in regard to the 
influence of temperature, because he used too many individuals, 
whose numbers in proportion to the food supply determined 
the conditions of nutrition that exist. Maupas may also 
have judged the sex of the offspring from the size of the egg. 
This is not always possible, according to Nussbaum; for while 
it is true that the biggest eggs become females, and the smallest 
males, there are many of each kind whose sizes overlap. 
Temperature favors the appearance of the males in so far as 
each animal lives at a higher rate at a higher temperature and 
needs more food, also at the higher temperature the output of eggs 
is faster, hence the food conditions poorer. Ata lower tempera- 
ture the output is slower and food conditions are relatively better ; 
but since the kind of egg produced is determined before the first 
egg is laid, it is not obvious that this criticism is apropos. 
Plenty of food during the development of the ovary leads to 
