18 



Bulletin 332 



The above experiments show that the outer, semi-transparent 

 brittle layer of the egg is permeable to water and cannot conserve 

 the moisture content of the embryo when exposed to adverse dry 

 conditions, but it does conserve a sufficient quantity of moisture 

 under normal out-of-door conditions, so that 25 per cent or more of 

 the eggs hatch. These experiments also indicate that the eggs are 

 most susceptible to drought just previous to the hatching period. 

 This is apparently due to the fact that almost all the normal eggs 

 preparing to hatch show a split outer covering and this splitting of 

 the outer shell exposes the permeable pigmented layer to adverse 

 conditions, thus increasing the rate of evaporation. 



A simple experiment was conducted to determine the relative 

 permeability of the pigmented layer and the outer semi-transparent 

 layer. The outer layer t was carefully removed from 15 normal 

 eggs of A. avenem on April 5, and the plump-skinned eggs were 

 transferred to a Syracuse watch glass with a piece of blotting paper 

 on the bottom. Fifteen normal plump eggs also were placed in the 

 same watch glass and a piece of moist blotting paper was addedi, 

 but this did not come in contact with any of the eggs. A similar 

 watch glass was used as a cover. 



TABLE 2 



Influence of Moisture on Skinned Eggs and Normal Eggs 



♦Observations made between 48 hours and 8 days omitted from table. 



The results from these experiments are conclusive; the pig- 

 mented or second layer about the egg is very permeable when 

 compared with the outer semi-transparent layer, for the water con- 

 tent of all the skinned eggs was completely evaporated in 24 hours. 

 The normal eggs were much more resistant, for in 24 hours only 

 two eggs showed a slight indication of shriveling, none of the skin- 

 ned eggs hatched, while 6 of the 15 normal eggs hatched in 4 days. 

 In brief, this experiment shows that the l)rittle outer layer acts as a 

 preventive agent against water evaporation under normal conditions, 

 while the inner pigmented layer does not perform this function to 

 any great extent. 



Under out-of-door conditions the percentage of hatch of the 

 eggs of A. avencB has been observed for two seasons. In 1917 



