Séance du 16 Avril 1924 
155 
G. capitata has not in nature clearly divided 
generations and it is possible to find in sub-tropical 
and tropical countries from spring till autumn all 
stages of the flly side by side. Therefore it is impos¬ 
sible to fix the development data exactly to the day. 
It is only possible, firstly to give an ideal view on the 
development possibilities of G. capitata under given 
climatica! conditions and secondly by this means ta 
give to the applied entomologist a good basis for his 
observations. 
We may climatically divide the countries which are 
infested with G. capitata as follows : 
1. —Countries, where is no possibility of perma¬ 
nent acclimatisation. Occasional seasonal attacks may 
occur but only from imported flies. The type for this 
category is England. 
2. —Countries, where G. capitata is permanently 
established, but the continuation of generations is 
interrupted by a development-duration of at least ioo 
days in the winter generation. 
Such are Southern Europe, the Mediterranean 
region, South Africa, the cooler parts of Australia and 
California. 
3 . —Countries, where one generation follows the 
other without interpolation of a winter generation. 
The average temperature here is never below i 3 , 5 ° C. 
Such are the tropical regions. 
By means of the data of table i I followed the 
development of G. capitata in Palestine, 
