378 THE NATURAL HISTORY 



caterpillar, that of the White Cabbage butterfly. These 

 masses are often very conspicuous under the copings 

 of walls, the bars of greenhouse lights, in tool houses 

 and garden sheds, where the infested caterpillar has 

 fixed itself preparatory to its final transformations, hap- 

 pily unconscious of the fact, we presume, that it contains 

 within its own system a host of tiny foes that are only 

 awaiting the appointed time to ' bring its " strange 

 eventful history" to a close. In the early stage of their 

 subcutaneous existence, these parasitic grubs subsist on 

 the fatty matter alone of the caterpillar, without in 

 any way impairing its appetite, or impeding its growth, 

 but when the latter has ceased feeding, they un- 

 scrupulously attack its vital parts and speedily cause 

 its death. They then make their way out through its 

 skin, spin themselves up in their silken cocoons, and 

 eventually become perfect four-winged flies, capable of 

 repeating the process to which they owe their own 

 development on the next generation of caterpillars. 



Campoplex paniscus we have bred from the larvae of 

 a minute moth of which we shall give some account 

 further on. Another genus of ichneumons is parasitic 

 on the plant-lice, and is hence named Aphidius. The 

 species of this genus undergo all their transformations 

 within the skin of the aphides, which, after the whole of 

 the interior has been devoured, becomes dry and rigid 

 like that of an ordinary pupa, and, wonderful to relate, 

 other parasites of the same order actually deposit their 

 eggs through this skin into the body of the included 

 parasite ! The history of these insects abounds with 

 similar examples, a phenomenon which has been im- 

 mortalized by an anonymous poet in the following 

 deservedly-admired couplet : 



" The little fleas that do so teaze, 



Have smaller fleas that bite 'em, 

 And these, again, have lesser fleas, 

 And so, ad infinitum? 



The family of parasites immediately succeeding the 



