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94 Bulletin of the Brooklyn Entomological Society Vol. XIV 
Period, a mild uniform climate prevailed almost to the pole, in 
all probability without frost or dry seasons, and the insects of 
this period are predominantly those with incomplete meta- 
morphosis. At the beginning of the Mesozoic Period, the climate 
became changed and, according to Handlirsch, caused the appear- 
ance of holometabolism, since several holometabolous groups 
such as the Coleoptera, Neuroptera, Mecoptera, etc., make their 
appearance at this time. Handlirsch would claim that the ap- 
pearance of cold, through the influence of the seasons, shortens 
the feeding and growth period, and allows insufficient time for 
insects to develop gradually, thereby bringing about the inser- 
tion of a resting stage during which wings and many other parts 
of the body rapidly develop. He also considers that the an- 
cestors of winged insects were aquatic. 
If Handlirsch had not attempted to so present his figures as 
to give the wrong impression—in other words, if instead of say- 
ing that 30 per cent. of the Coleoptera, 4o per cent. of the 
Hymenoptera and 50 per cent. of the Diptera occur in temperate 
climates, he had set forth the figures in their true light, namely 
that 70 per cent. of the Coleoptera, 60 per cent. of the Hymen- 
optera and 50 per cent. of the Diptera occur in warm climates— 
these figures if they have any meaning at all, would clearly indi- 
cate that holometabolism originated in warm climates where most 
of the holometabolous forms occur! The Coleoptera are the 
most primitive of the holometabolous forms mentioned, and most 
of them occur in the warm climatic conditions where they origi- 
nated, as one would expect to be the case. The Hymenoptera 
are slightly more highly developed than the Coleoptera, and being 
somewhat more adaptable forms, have been able to establish 
themselves in somewhat greater numbers than the Coleoptera, in 
the temperate regions. On the other had, the Diptera are the 
highest of the metabolous insects mentioned—in other words, the 
latest comers to arrive upon the scene—and are also very numer- 
ous in species, apparently highly adaptable, and possibly are in a 
more “active state of evolution” (1. e., producing more features 
to be acted upon by natural selection). The Diptera have there- 
fore been even better able to establish themselves in the “inim- 
ical” regions of cold than the more primitve members of the 
