262 TRANSFORMATIONS OF INSECTS. 



perfect insects cither fly in the air or crawl on dry land. Immer- 

 sion in water is fatal to them after a time. The larvae of many 

 Ichneumons appear to exist surrounded by the juices of their 

 victims, and they must respire either by means of the air passing 

 through the air tubes of the insects they live in, or by the more 

 or less aerated fluids which form their nourishment. But the 

 majority of the hymenopterous larvae respire by spiracles, and 

 cannot live under water. 



A discovery of Sir John Lubbock's is, therefore, very inte- 

 resting. He observed many specimens of a small hymenopterous 

 insect swimming in pond water with their wings, and quite at 

 their ease. The fly belonged to a genus the larvae of which are 

 eminently parasitic in the eggs of some Lepidoptera ; and the 

 accomplished naturalist just mentioned considers it highly pro- 

 bable that the slow-flying swimming insect was in. search of some 

 aquatic victims for its progeny. He found a second species, 

 which used its legs as oars, but did not swim with its wings ; 

 and he noticed that both kinds of these PolynemcE were fond of 

 creeping along the sides of the vessel in which they were placed, 

 or on the leaves and stems of aquatic plants. They frequently 

 swam boldly out into open water. The history of the metamor- 

 phosis of these aquatic Hyuienoptera has yet to be written ; and 

 it is evident that its comparison with that of the HydrocampidcE 

 amongst the Lepidoptera will form a most interesting inquiry. 



The metamorphoses of the Hynicnoptera differ from those of 

 the Lepidoptera, in consequence of the larva remaining for a 

 greater or less period inside a cocoon before transforming into a 

 pupa. Instances of retrograde metamorphosis appear to occur 

 in the genus Cy?iips, and the wingless condition of the female 

 members of the species of Cynips terniinalis, and the absence of 

 wings in Cynips aptera, are usually stated as examples. But 

 the metamorphosis can hardly be said to be retrograde in the 

 strict sense of the term, for the perfect female of Cynips terniinalis 

 and the adults of both sexes of Cynips aptera are more fully 

 developed than their larvae and nymphs, and possess additional 

 structures. In no sense can they be said to be lower in the insect 

 scale. 



The transformations of these insects are not then retrograde, 



