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moults ; it has no quiescent stage like the chrysalis of a moth or 

 butterfly, neither does it change its food, its mouth organs having 

 always the same form. 



Eegarding the natural history of these insects comparatively 

 little is known, and it is very difficult to keep them alive in 

 confinement. 



Most insects, probably all, have their parasites. I have not 

 looked for them much among the Heteroptera, and all I have yet 

 noticed belong to the genus Scirus (snouted mites). Among the 

 water bugs I have frequently found Gerris Gibbifera, with its 

 colour changed from that of black velvet to a brilliant scarlet by 

 the number of these parasites* that had fastened themselves to it. 



I said that most insects had their parasites, two specimens of 

 which I have brought to show you. The first is one of the 

 Hymenoptera, Trichiosoma lucorum. The parasite, an ichneumon 

 fly, lays a number of eggs in the body of the larva of Trichiosoma. 

 This larva looks very like a green caterpillar, and unless looked 

 at closely might easily be mistaken for the larva of a butterfly or 

 moth ; but whereas the true caterpillar has never more than 16 

 legs, this larva has 22. These eggs soon hatch into little white 

 maggots within the body of the lan'a, and reach their full 

 development by feeding on its substance, and they are endowed 

 with a wonderful instinct which prevents their attacking any vital 

 part, and so killing their host, for in this case they would die also. 

 The larva therefore is left with sufficient strength to form its 

 cocoon, but having done so it dies, and the small ichneumons, 

 which belong to the same order of insects, the Hymenoptera, 

 proceed to make their own cocoons within it, where they remain 

 until the following spring, when they appear as the fly you see by 

 its side. 



This is an example where the parasites are large, and where 



* I have not examined these ; they probably belong to a different 

 family. 



