Life Cycle of Hydatina Senta 343 



Experiment XIV. Over a hundred fertilization experiments 

 were made to test this point. Young females within the first 

 six hours after hatching were placed in several drops of water 

 with a few vigorous males about a day old. They were watched 

 until copulation occurred, then separated by taking them up in 

 a pipette and squirting them vigorously out again. The time 

 of copulation varied from 2 to 25 seconds. But from every one 

 of these females that did not produce females parthenogenetically, 

 I obtained only resting eggs or only male eggs. Some of the fer- 

 tilized females laid small eggs toward the last of their output, 

 often not any larger than the majority of male eggs; but these 

 eggs had the thick shell and characteristic markings of winter 

 eggs, and they did not hatch even when kept for days, so they were 

 classed as resting eggs. 



Later, a number of fertilized females were reared for cytological 

 study. The method of securing them was as follows: A female 

 was isolated and allowed to produce at least one daughter to show 

 that she was a female-producer. There was then placed in the 

 dish with her a male-producer that had been producing young for 

 some hours, together with the 12 to 15 males which had already 

 hatched from her eggs. As the young females hatched in this 

 dish, they nearly all copulated, and were isolated at intervals as 

 as in the other experiments. It thus happened that the male- 

 producer was always about a day older than the female-producer 

 in the same dish, so that the males wereold,orsometimes all dead, 

 when the last females of the family hatched. These late females 

 were sometimes not fertilized, and produced males. 



On September 9, 1909, a young female, the last member of a 

 family of 46, hatched under the conditions described above, and 

 was isolated. On September 10 she had laid two large eggs, of the 

 shape of resting eggs; but though their shells were thicker than 

 those of parthenogenetic eggs, they were considerably thinner 

 than those of most resting eggs. Without examining them care- 

 fully with a microscope, to determine the markings of the shell, 

 I set the dish aside to see whether the eggs would hatch in a few 

 hours, as they probably would if they were parthenogenetic eggs. 



