Ì54 Bulletin de la Société Royale Ëntomologique d'Egypte 
There are some restrictions for the use of this 
Table. The critical cold-point and the unknown cri¬ 
tical heat-point may be exactly established only by 
the use of Pierce’s combined temperature-humidity 
method. I am considering the critical cold-point of 
the above formula only as a useful provisorium, prior 
to the difficult fixation of the empirical Pierce-data. 
There are great differences of air humidity in the 
countries under discussion. Here are tropical coun¬ 
tries, which are nearly saturated with waterdamp and 
others, which are more or less arid This is the first 
uncertainty in this case. The second uncertainty is 
the impossibility to estimate whether any short period 
remaining before the beginning of winter will be 
sufficient for the development of another generation 
or not. 
Examples are Plymouth and Naples We have to 
remember that i 3 , 5 ° G is the critical cold-point. At 
Plymouth, the development of the summer genera¬ 
tion lasts from the middle of June till the beginning 
of October. But the temperature of the first half of 
June (i6,8° G) is not sufficient, considering the aver¬ 
age temperature of 8,i° C in the other months, to 
make possible a winter generation. This means that 
there is no probability, that the acclimatisation of the 
fruit-fly in England will be possible. Whether the 
development of another generation at Naples (Portici) 
should be possible, depends on the development of 
the previous generation, if it is finished in the last 
decade of September or only in the first of October. 
Actually there are developing numerous specimens in 
October, which fact could not be established by es¬ 
timation. 
