THE FUNDAMENTAL FACTOR OF INSECT 

 EVOLUTION. 1 



By S. S. Chetveeikov. 



[With 1 plate.] 



The question of how this evolution traveled, which factors directed 

 it along the course that led insects to their present height of organiza- 

 tion, is of deep interest to every entomologist. 



Insects appeared on the earth very long ago. Beginning with the 

 middle of the Paleozoic era — namely, the Carboniferous period — the 

 earth's crust contains undoubted traces of insects, principally impres- 

 sions of wings, and indications of insects exist even in the earlier 

 epochs. And thus, in course of this colossal interval of time, an 

 interval the greatness of which is beyond the limit of human under- 

 standing (be this interval 30,000,000 or 60,000,000 years, the impres- 

 sion on the mind will not be different), the process of evolution of 

 the insect forms continued unabated — a process which brought them 

 to the present stage. The tremendous development attained by insect 

 life on earth is best shown by the following few figures. By 1907, 

 384,000 species of insects were described and named. An annual 

 average of about 6,000 species is being described since then, a num- 

 ber which shows no tendency to diminish; on the contrary, as 

 Europeans penetrate into tropical countries, this number is showing 

 decided increase. Thus, all agree that the number of species of 

 insects on the earth must be expressed by a number of at least seven 

 figures. But, whichever the number we finally agree upon, whether 

 that of 10,000,000 species by Riley, or the more modest figure of 

 2,000,000 by Sharp, one fact remains certain — namely, that the num- 

 ber of species of insects is at least six times that of species of all the 

 ether animals put together. And, if we recall that the number of 

 individuals of each species of insects is on the average many times 

 greater than that of other species of animals (excepting Protozoa), 

 the colossal development of animal life in the form of entomons will 

 become fully evident. 



What is the cause of this ? What is there in the insect that gave it 

 the capability of occupying this exclusive position in the animal 



1 Translated from the Russian by Jacob Kotinsky, Branch of Forest Insects, Bureau of 

 Entomology, U. S. Dept. of Agriculture, from Bull. Soc. Ent. Moscow, Vol. I, p. 14, Nov. 

 (15) 28, 1915. 



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