AND THE LOWER ANIMALS. 71 



insects in which there are three distinct stages of 

 existence, corresponding to the larva, nymph or pupa, 

 and perfect form or imago. But if we compare it with 

 our ideal type, we shall see that an insect, although 

 passing through these three stages, may yet want one 

 of the essential characters already referred to. Thus, 

 its last transformation may be as it were arrested at a 

 certain point, and consequently the metamorphosis 

 may be in reality incomplete. There is a sort of tran- 

 sition to those species whose changes are consecutive, 

 slightly marked, or even absent. 



With such exceptions we may look upon the follow- 

 ing groups as insects which undergo complete meta- 

 morphoses — the Neuroptera (dragon-flies, day-flies, 

 and white ants) ; the Hymenoptera (bees and wasps) ; 

 the Coleoptera (beetles, lady-birds, &c.) ; and, finally, 

 the Lepidoptera or butterflies. Having done with the 

 latter, we shall now give a brief sketch of the other 

 orders, and in doing so contrast the more remark- 

 able points in their life-history with the facts already 

 detailed.* 



memoir on the metamorphoses of strepsiptera (Wieginann's Archiv, 

 1843), and M. Joly, in his "Becherches zoologiques, anatomiques 

 et physiologiques sur les QEstrides," 1846, have pointed out similar 

 facts. The latter proved, moreover, that the anatomical changes and 

 alterations of external form are simultaneous. He very correctly 

 ascribes these phenomena to the conditions of life which the para- 

 sitic habits of the insect bring with them. — " Note sur i'Hypermeta- 

 morphose des Strepsipteres et des OEstrides," Comptes rendus, 1848. 

 * These metamorphoses do not always take place in the same 

 manner in different orders. We may find a sub-order present- 

 ing peculiarities of its own, and even the individuals which 

 it comprises may differ from each other as to the way in which 

 these changes occur. Although limited as to the selection of 

 species, I have chosen those which follow the general plan as closely 



