THE STUDY OF INSECT LIFE 21 



far to trace the gradual development from the 

 simple primitive type to the more complex 

 forms, by the remains that have been found in 

 the various strata. Nevertheless, these geological 

 records do most clearly show us that insects 

 appeared very early in the history of the earth, for 

 the wing of an insect similar to the Cockroach has 

 been found in the Silurian strata, while ancestral 

 Dragon-flies and Lacewing-flies, only slightly less 

 specialized than the present existing forms, have 

 also been found. In the Coal-measures, not only 

 do we find fossil remains of Coleoptera and 

 Hemiptera, but the fossil leaves and tree-trunks 

 show unmistakable signs of the ravages of 

 insects. Fossil remains of species of the 

 Hymenoptera and Diptera are found in the 

 Jurassic Period, and of the Lepidoptera in 

 the Tertiary beds. 



If, in attempting to link up the gaps between 

 the simplest and most specialized forms of insect 

 life, we turn our attention to the embryology 

 and development of still existing forms, we are 

 at once impressed by the extraordinary similarity 

 that exists in the general anatomical details in 

 the embryonic and larval stages, between species 

 which in the adult stage are quite dissimilar. 

 Thus, as Lord Avebury has ably stated, "we 

 find in many of the principal groups of insects 

 that, greatly as they differ from one another in 

 their mature condition, when they leave the egg 

 they more nearly resemble the typical insect 

 type; consisting of a head; a three-segmented 

 thorax, with three pairs of legs; and a many- 

 jointed abdomen, often with anal appendages. 



