ENTOMOLOGY 



10. Direction indicated by the annual migration routes, in 

 birds (Palmen). 



2. GEOLOGICAL 



Means of Fossilization. Abundant as insects are at pres- 

 ent, they are comparatively rare as fossils, the fossil species 

 forming but one per cent, of the total number of described 

 species of insects. The absence of insect remains in sedimen- 

 tary rocks of marine origin is explained by the fact that almost 

 no insects inhabit salt water; and terrestrial forms in general 

 are ill-adapted for fossilization. The hosts of insects that die 

 each year leave remarkably few traces in the soil, owing per- 

 haps, in great measure, to the dissolution of chitin in the pres- 

 ence of moisture. 



Most of the fossil insects that are known have been found 

 in vegetable accumulations such as coal, peat and lignite, or 

 else in ancient fresh-water basins, where the insects were prob- 

 ably drowned and rapidly imbedded. At present, enormous 

 numbers of insects are sometimes cast upon the shores of our 

 great lakes a phenomenon which helps to explain the profu- 

 sion of fossil forms found in some of the ancient lake basins. 



Insects in rich variety have been preserved in amber, the 

 fossilized resin of coniferous trees. This substance, as it 

 exuded, must have entangled and enveloped insect visitors just 

 as it does at present. Many of these amber insects are ex- 

 quisitely preserved, as if sealed in glass. Copal, a transparent, 

 amber-like resin from various tropical trees, particularly Legu- 

 minosae, has also yielded many interesting insects. 



Ill-adapted as insects are by organization and habit for the 

 commoner methods of fossilization, the number of fossil spe- 

 cies already described is no less than three thousand. 



Localities for Fossil Insects. The Devonian of New 

 Brunswick has furnished a few forms, found near St. John, in 

 a small ledge that outcrops between tide-marks; these forms, 

 though few, are of extraordinary interest, as will be seen. 



For Carboniferous species, Commentry in France is a noted 

 locality, through the admirable researches of Brongniart, who 





