196 THE THEOKY OF EVOLUTION 



systematic species, genera, and families such as we 

 find to-day. 



An example out of the class of insects we give in 

 more detail. The order of the Beetles appeared geo- 

 logically already in the beginning of the Mesozoic 

 group of formations in the Trias, where it is represented 

 by about twenty genera. Altogether 352 Mesozoic species 

 of beetles have long since been found. 1 The order of 

 the Termites (Isopterae) appears, however so far as 

 hitherto can be certainly known first in the beginning 

 of the Tertiary period, therefore at the commencement 

 of the Csenozoic group of formations : in the Eocene we 

 find first one species, in the Oligocene twenty -five, in the 

 Miocene twenty-nine. The family of the Ants of the order 

 of Hymenoptera, so far as can be certainly known, first 

 appeared in the lower Oligocene thus in the older 

 Tertiary period : in the Oligocene there are 121, in the 

 Miocene 174 species which for fossil insects is a very 

 large number. 2 In any case we see from this that 

 both the Ants and the Termites only, in the beginning 

 of the Tertiary period, became a power in the household 

 of the world, which was the essential preliminary con- 

 dition for the adaptation of other insects to the mode 

 of existence in the nests of the Ants and Termites. We 

 must therefore necessarily assume that the myrmecophil 

 and termitophil species, genera, and families of the 

 Beetles either were first subsequently created in the 

 Tertiary period and that means each species, genus, 



1 Handlirsch : Die fossilen Inseckten, pp. 398, 1171. 



2 Ibid. 1182, 1185. 



