446 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1918. 



age: Meganewa monyi Brongn., order Protodonata. Alongside of 

 it (lower right), reduced to the same scale, is its contemporary 

 progeny, Aeschna grandis L. What a pitiful pigmy it is and its 

 specific name (gmndis) sounds like such a mockery. 



Such are the giant Paleozoic insects. 



Handlirsch's conclusion that the existence of gigantic forms is 

 explainable by the fact that they lived in a tropical climate is, in my 

 opinion, entirely wrong. I cheerfully admit that in those remote 

 times the climate of the center of contemporary France, where most 

 of the excavated insects lived, might have been tropical, but we have 

 absolutely no proof that this has any causative relation to the large 

 size of the Paleozoic insects. 



Handlirsch himself admits that myriads of extremely small forms, 

 the like of which did not exist in the Carboniferous epoch, exist in 

 the present tropics alongside of the larger ones (though still not as 

 large as the Paleozoic) . I am firmly convinced that the question here 

 is not of climate, but of the fact that here we have only the begin- 

 ning, the dawn of insect evolution. 



And now we pass over to the Mesozoic. Here the general appear- 

 ance of the insects changes very abruptly. All contemporary orders 

 and even many of the contemporary families have their represen- 

 tatives there. I will not stop to enumerate; I will merely indicate 

 that insects with complete metamorphosis appear for the first time 

 in the Mesozoic. If we compare the Mesozoic fauna with that of 

 the Paleozoic just described, and then with the contemporary, the 

 first will be found to contain probably more in common with the 

 latter than with the extinct giants that inhabited the Carboniferous 

 landscape. And alongside of the already quite definite specializa- 

 tion in the Mesozoic forms there appear also small, inconspicuous 

 species which attain sometimes barely 3 millimeters in size, but their 

 impressions are still preserved quite clearly. 



I call attention to another fact which is associated with the same 

 evolutionary tendency of insects: Four of the contemporary orders 

 (Coleoptera, Lepidoptera, Ilymenoptera, and Diptera) have de- 

 veloped particularly rapidly in the geological epoch nearest to us. 

 It also appears that just these four orders are particularly rich in 

 small forms. This fact tells us clearly that the evolution of forms, 

 directed towards a diminution in size of body, leads in insects to a 

 rapid development of the orders mentioned. The new forms do not 

 crowd the old ones out ; they merely take that which the old ones for 

 some reason were incapable of utilizing. On the other hand, in 

 those orders like the dragon flies and Orthoptera, for instance, in 

 which, by virtue of some inherent causes, the process of diminution 

 developed slowly, the entire evolution also proceeds in a slow tempo, 



