124 Bulletin de la Société Royale Entomologique d'Egypte 
both ‘a’ and ‘b', though at different ends of the 
series. With the exception of a few irregularities to be 
discussed a little later, the intervals between oviposi- 
tions during July, August and the beginning of Sep¬ 
tember are 4 or 5 days. 
Vigorous individuals will go on laying at short 
intervals until the end of the month of September and 
in some cases even later so that the increase in length 
of the intervals must be attributed, at least in part, 
to individual differences in the females. There is also 
a more or less marked tendency to slow down towards 
the end of the egg-laying period. These two factors 
are even more marked in the case of unfertilized 
females, so that it is very difficult to estimate exactly 
the share of each and to fix a critical date when the 
approach of winter begins to make itself felt. This is 
especially so in the case of the females on the study 
of which this note is based, for they all moulted for 
the last time in July and the majority of the egg-cases 
were made before the end of September. 
In TV, however, the effect of the cold is clearly 
marked. The first four egg-cases of N° 3 were laid 
from the 23 rd of January to the 24th of March 1916 
and the first seven of N° 3 i 5 from the i 3 th of Decem¬ 
ber 1916 to the 20th of April 1917. The differences 
shown in the table need no further comment. 
Under optimum or nearly optimum conditions, 
such as those under which these insects were bred, 
irregularities due to individual differences are slight 
and barely noticeable. There is nothing in the post- 
embryonic development of the five females which 
could suggest any explanation of the marked irre- 
