OF WASHINGTON. 331 



clearly marked regional divisions of the body ; this is a consid 

 eration of great significance, since in the progress of structure, 

 from the worms, through the crustaceans to the insects ; or with 

 the progress of structure, from myriapods, through the arach 

 nids to the hexapods ; or in the developmental history of the 

 Metabola themselves, from the larva, through the pupa to 

 the imago, we discover constantly increasing concentration of the 

 segments of which the body is composed into distinct regions, 

 culminating in the Hymenoptera, where head, thorax, and abdo 

 men are most sharply defined." 



All the orders of the Heterometabola and none of the Metabola 

 are represented in the palaeozoic rocks. Scudder states: "This 

 is the more striking from the fact that if we omit mention of the 

 single discovery of insect wings in the Devonian, the three orders 

 of insects hexapods, arachnids, and myriapods appear simulta 

 neously in the Carboniferous strata. The Metabola are then 

 later in time and more perfect in development than the Hetero 

 metabola." 



Packard also believes the Hymenoptera are descendant from 

 the Lepidoptera. 



Thus we see that most authorities are agreed as to the affini 

 ties existing between the Hymenoptera and Lepidoptera, and 

 there is scarcely any doubt in my own mind now that this is the 

 correct view, and that these two orders with the Trichoptera 

 and part of the Diptera had a common ancestry. 



This relationship is shown in the close resemblance between 

 the larvae of the phytophagous Hymenoptera and those of cer 

 tain lepidopterous larvae, although the direct line of descent 

 cannot be pointed out absolutely. 



The relationship will probably be found among some of the 

 wood-boring Lepidoptera, Cossidce, sEgeriidce, Hepialidce, 

 etc., and more particularly among those lepidopterous insects 

 furnished with an ovipositor. 



The larvae of the Mecaptera (Panorpidae) also approach close 

 to the Hymenoptera, and the peculiar rostrate head of the imagoes 

 of this order is frequently reproduced among the parasitic species 

 (Agathis, Cremnops, etc.). 



Mr. Nathan Banks has suggested that the Megaptera were the 



