EFFECT OF ENVIRONMENT UPON HYDATINA SENTA. 



343 



the dishes, ranged from 2 to 12 C. The air temperature was 

 much below this, but was moderated in 'the location of the eggs 

 by a steam radiator near the window sill inside. It appears that 

 the water in which the eggs were placed never froze and hatching 

 occurred during this period of low temperature. From Decem- 

 ber 22 to December 25 the atmospheric temperature was con- 

 siderably above freezing but was much colder thereafter. On 

 January 3 the "cold" dish was removed to room temperature, 

 but hatching had been nearly completed before that time. 

 Table VIII. shows the number of eggs that hatched. 



TABLE VIII. 



Showing the Effect of Room Temperature and Lower Temperatures Upon the Hatching 

 of the Fertilized Eggs of Hydatina Senta. 



Low temperature appears to favor the hatching of the eggs, 

 not as an after effect, but during the period of low temperature. 



Effect of Oxygen upon the Viability of the Fertilized Eggs. 



Each of four lots of eggs from a single source was divided into 

 two equal parts. One was placed in water of high oxygen con- 

 tent (saturated with an atmosphere of which either 40 per cent, 

 or 60 per cent, was oxygen) and set under a bell jar enclosing an 

 atmosphere containing the same proportion of oxygen as that 

 with which the water was originally saturated. Atmospheres 

 of 40 per cent, oxygen were used until July 7, 60 per cent, there- 

 after. This dish was removed from the bell jar daily and exam- 

 ined for hatching rotifers. The water was drawn off the eggs 

 after examination and replaced with fresh oxygenated water 

 and the dish returned to the bell jar. 



