Lepidoptera — Hymenoptera 361 



of the imago it is found that in three families of 

 moths (Micropterygidff, Eriocraniidae, and Hepialidje) 

 the neuration of the hind-wings is as complex as 

 that of the fore-wings, at whose base is a fold in 

 the membrane (jugum); these features are char- 

 acteristic of the Caddis-flies. There seems no doubt 

 therefore that the Lepidoptera must be derived from 

 Trichopteroid ancestors. And the difference in the 

 larval structure and habits shows clearly that the 

 primitive moths diverged from the primitive caddis- 

 flies before the grubs of the latter had taken to an 

 aquatic life. Fossil remains of insects of these two 

 orders are extremely rare, but we know that moths 

 with sucking-tubes like those of modern Sphingidse 

 already lived in Oolitic times. The wing-neuration 

 of some of these Secondary insects was like that of 

 modern Cossidx, but it is only in Tertiary beds that 

 remains of Lepidoptera clearly referable to existing 

 families have been found. Fossil wings of insects 

 believed to have been Caddis-flies occur as early as 

 the Lias ; they resemble in their neuration the wings 

 from the same rocks which are referred to the 

 Panorpidse. And the Panorpidae — the only family of 

 Neuroptera with eruciform larvae — give us a hint of 

 the vanished insects which must have connected the 

 common ancestors of modern moths and caddis-flies 

 with the primitive Neuropteroid stock. 



Hymenoptera and Diptera. — The Hymenoptera 

 and Diptera must undoubtedly be regarded as the 

 most highly modified of all insects, the former order 

 in some respects, the latter in others, having reached 

 a farther degree of development. In the structure of 

 the jaws the Hymenoptera are comparatively primitive, 

 most of the families retain the biting mandibles ; and 

 the specialised sucking and working mouth-parts of 

 the higher Bees are formed by enlargement or reduc- 



