-2 WYMAX REED GREEN. 



my attempts to discover a means of ending the latent period, 

 . i h hough in not a single instance have results been all that could 

 be desired. In a considerable number of my experiments I 

 have made special effort to reproduce the factors operating upon 

 these eggs in nature, by a series of freezings, alternate! 1 with 

 drying, placing the eggs in the sunlight, etc., but the results 

 seem to indicate that I have neglected the one thing needful. Of 

 one thing I am quite certain, namely, that the fact that the eggs 

 of Simocephaliis vetnlus can be collected from the fresh-water 

 ponds every month in the year must be taken into account in 

 formulating any general conclusions as to the factors concerned 

 with their development. Unless otherwise stated, eggs of 

 Simo&phalus vetulus were used in the following experiments. 

 In experiments performed with eggs collected from the field there 

 were usually several kinds present but those of Simocephalus 

 predominate. My only successes have been with Simocephalus 

 eggs which were produced in the laboratory. 



Experiment I. Since the eggs that are laid in ponds are, as 

 the ponds dry up, subjected to graduallly increasing concentra- 

 tions of whatever salts may be in solution in the pond water 

 it occurred to me that this might be a potent factor in terminating 

 the latent period. To test this I took numerous ephippial eggs 

 from my laboratory cultures and placed them in a pint of pond 

 water and allowed it to stand exposed in the laboratory in a 

 wide stender dish. I placed a graduated scale on the side of 

 the dish, dividing the water depth into ten equal spaces. When 

 the water had lowered to each of the various levels by evapora- 

 tion, I took out a number of the eggs and placed them in covered 

 vessels. Continuing thus until the water in the open dish had 

 all disappeared, I left the last lot in the open vessel until it 

 was thoroughly dry. The same experiment was tried starting 

 with low concentrations of XaCl, but the results were negative 

 in all cases. 



Experiment 2. A large number of ephippial eggs were col- 

 lected from the surface of the ice on temporary ponds near 

 Gary, Ind.. on March 12, i<>i4, and dried at once. On June 

 1916, they were placed in water at room temperature and 

 They were watched for several months until it seemed 



