1920] Peterson: Hatching of Aphid Eggs 393' 



moisture generator, one or more air chambers and a pump. 

 The moisture generators and the air chambers were located in 

 the incubators and kept at a constant temperature; 80° F. 

 in 1917 and 70-72° F. in 1920. The air was taken from the 

 room and first passed through the two tubes of sulfuric acid 

 (Specific Gravity 1.84), which removed all of the water. The 

 dry air was then drawn through concentrated salt solutions and 

 a constant amount of water was absorbed by the dry air. The 

 moisture content of dry air after it passes through concentrated 

 salt solutions varies with different salts, but the same salt 

 always gives up a definite amount of moisture. This was 

 determined for each salt a number of times and each test- 

 showed less than 0.5 per cent variation in the water present. 

 The air goes from the moisture generator to the air chambers, 

 where the numerous eggs were located on short twigs. Small 

 twigs bearing numerous eggs were selected in order that the 

 moisture arising from the freshly cut twigs would have as little 

 influence as possible on the moisture content of the air. It 

 is believed that the small amount of moisture arising from the 

 twigs had very little effect; if the moisture in the twigs effects 

 the air in the chambers the effect is of short duration, for it 

 was noted that the twigs in the chambers having low moisture 

 content dried and shriveled in two or three days, while the 

 eggs usually required ten to fourteen days to hatch after they 

 are placed in the air chambers. The air was drawn from the 

 air chambers by a small pump, which was operated by flow- 

 ing water. 



' Table 1 shows the influence of various constant percentages 

 of moisture on the eggs of A . avencB and A . pomi. The dates at 

 the top of the columns indicate the day the experiments were 

 started. The percentage of hatch varies with the moisture 

 content; the greatest percentages of hatch occur in airs 

 possessing a large amount of moisture, while low percentages 

 of hatch occur in airs possessing small amounts of moisture 

 and usually no hatch in dry air. Some of the eggs in the 

 above experiments had split their outer coats when the experi- 

 ments were started. In the dryer airs these eggs shriveled 

 rapidly and failed to hatch. 



In 1917 eggs of A. pomi were placed in the incubators early 

 in March, but this is too early for this species. For some unknown 

 reason one cannot get a normal percentage of hatch of the eggs 



