134 Bulletin de la Société Royale Entomologique d'Egypte 
have not included them in any of the preceding 
tables or arguments in order to avoid confusion. 
8. The Incubation Period. 
The Incubation period varies from 16 to 91 days; 
in one case to be discussed later it was only i 3 days. 
For egg-cases laid by the mother from 28.1.16 to 3 o. 5 .16 
the incubation period diminished regularly from 79 
to 22 days. Here I may point out that the fact that 
no young emerged from egg-cases laid after the 
middle of November must not be attributed entirely 
to the cold but also to the worn out condition of the 
females. Many egg-cases laid during July and August 
gave no emergences, and on the other hand the egg- 
case laid in January by the mother gave a few young. 
Temperature being by far the most important 
factor in determining the length of the egg-stage, it 
would be necessary to take the date of laying of each 
egg-case into consideration in tabularizing the data. 
As laying went on for six months, such a table is 
not possible here, and the fact that the young from 
one egg-case did not come out at the same time in 
the majority of cases further complicates the matter. 
Whenever there has been a relatively large emergence 
from one egg-case, 1 have considered the day on 
which it occurred as the date of hatching, in other 
cases, I have taken the average. In the case of the 
fertilized females I have already shown that the 
stragglers are not of much importance and, so far 
