Life-cycle of the Rotifer ; Hydatina Senta 347 



in fact, they do not appear at all unless previous union with 

 a male has occurred. 



Maupas found that of 796 females isolated from males only 

 parthenogenetic eggs were produced (male or female). Of 172 

 females to which males had been added at the right time (about 

 6 hours after hatching), 84 produced winter eggs and %'^ 

 parthenogenetic eggs (male or female). In another experiment 

 822 females were used, and 342 of these were observed to unite 

 with males. Of these (342) there were 252 that laid winter eggs, 

 the other 90 produced summer eggs. The ratio of individuals 

 laying winter eggs to those laying summer eggs is, therefore, 74 

 to 26. The remainder of the 822 females that were not seen to 

 pair, 480 in number, gave the following results: 361 produced 

 males and 119 produced females. The ratio is 75 to 25. This 

 is nearly the same ratio as the ratio of winter eggs to summer 

 eggs given above. From this similarity in proportion Mau- 

 pas concludes that only male eggs can be fertihzed, and these 

 become winter eggs. The winter eggs give rise solely to females. 

 If this conclusion is established, it follows that fertilization 

 changes the sex of the egg, as in the bee. Nussbaum believes the 

 similarity in the ratios may be purely accidental, but will not 

 deny that the conclusion may be correct. 



Maupas tried to show that temperature is the factor that 

 determines the fate of the eggs. If the temperature is lowered, 

 females are produced. If the temperature is raised, males are 

 produced. He gives the following experiment to establish this 

 conclusion. Five immature females were kept at a temperature 

 of 26° to 28° C. They laid 104 eggs, of which 97 per cent pro- 

 duced individuals that laid male eggs and only 3 per cent 

 produced individuals that laid female eggs. 



In the control experiment five immature individuals from the 

 same culture were kept at a temperature of 14° to 16° C. They 

 laid 260 eggs, of which 5 per cent became male and 95 pey cent 

 became female producers. It will be noticed that in these two 

 experiments both the mother and the eggs she produced were 

 under the same conditions of temperature, hence the effect 



