LIFE CYCLE OF SIMOCEPHALUS VETULUS. 73 



certain that none would develop. On August 15 the experi- 

 ment was discontinued. If freezing is the most important fac- 

 tor as some authors have believed, it certainly cannot be all 

 sufficient, for this lot of eggs numbered several hundreds and 

 they were frozen up in the ice for many weeks before they were 

 transferred to water. At two later dates other lots were col- 

 lected and treated similarly. The last was on March 21, when 

 the ice had begun to thaw. 



One lot of eggs taken from a laboratory culture in April were 

 dried for three days, then placed in water at room temperature 

 but did not hatch. After two months they were taken out and 

 dried. Over two years later they were again transferred to 

 water at room temperature without success. These experiments 

 were performed at the University of Chicago, but before leaving 

 there I secured great numbers of ephippial eggs by skimming the 

 surface of the ponds near Gary, Ind., and at intervals of every 

 few months thereafter for three years placed a number of these 

 in water. None ever hatched. The eggs treated in this way 

 w r ere not counted though 1,000 would be a very conservative 

 estimate. 



Experiment j . This experiment was performed with ephippial 

 eggs w r hich had been recently produced in the laboratory cul- 

 tures. They were subjected to very low concentrations of H 2 

 SO 4 , namely, M/ioo, M/io, M/5, M/2 and M/i, for I, 2, 10, 24 

 and 72 hours. Three eggs were used for each separate set of 

 conditions. The eggs were transferred to water and examined 

 daily. Results were negative. A precisely similar experiment 

 was then carried out with KOH in the place of the H 2 SO 4 , with- 

 out success. 



Experiment 4. On January 15, 1914, 10 ephippial eggs were 

 taken from a laboratory culture and dried for three hours, then 

 kept in a freezing mixture for eight hours after wrhich they were 

 transferred to water at room temperature. None hatched. 



On the same date 6 ephippial eggs were transferred directly 

 from a laboratory culture to water which was kept at 30 C. for 

 four wrecks. Another lot was kept at 28 C. Results were 

 negative in both cases. 



On January 18, 1914, some ephippial eggs which had been 



