LIFE CYCLE OF SIMOCEPHALUS VETULUS. 75 



alga? to nourish any embryos that might appear. They were 

 examined daily for some weeks and at intervals for two months. 

 Some of the eggs degenerated early and others persisted as if 

 no injury had been received. None had developed on October 

 10, and shortly thereafter no eggs could be found. 



Experiment 6. On January 15, 1916, two dozen eggs were 

 taken from a laboratory culture which had been producing an 

 abundance of them, and without being allowed to dry, \vere 

 placed in a vessel where the sun would strike them for a few 

 hours daily, for some weeks. They were then placed out of the 

 sun. On August 16 I placed them on ice for 24 hours, and then 

 left them until June, 1917. That they were in perfect condi- 

 tion at this time was shown by the fresh green color of the eggs 

 on removal of the ephippia. They were held under water by 

 being placed in a vial which was left lying on its side in a stender 

 dish. None of these developed. 



Experiment 7. On June 30, 1916, a number of ephippial eggs 

 of Daphnia pulex were taken from a laboratory culture and 

 placed under water in the same manner as in the above experi- 

 ment and left thus submerged until May 20, 1917- Dissection 

 of the ephippia from several of these showed them to be in good 

 condition at the end of this time, none having developed. 



Experiment 8. Although all of my carefully devised attempts 

 to induce ephippial eggs to hatch by the application of chemical 

 and mechanical stimuli, as well as the numerous repetitions 

 of the freezing experiments of Weismann, have completely failed, 

 I have succeeded in securing about 70 stem mothers from some 

 Simocephalus vetulus eggs which had been given no special 

 treatment. On June 27, 1916, I removed several hundred eggs 

 from a culture which had produced great numbers of them and 

 placed them in a large-mouthed 8 oz. bottle lying in a horizontal 

 position in a one-gallon battery jar about one third full of water. 

 A small amount of unicellular green algae was added. Cypris 

 of several species soon appeared in large numbers On August 

 14 an embryo of Simocephalus appeared. I removed it in a 

 little of the same water together with some of the algae. It 

 lived only three clays. Fortunately others were to follow. On 

 August 1 8 another appeared, and produced a brood of 7 females 



