PARASITE-INSECTS. 61 



It must have occurred to the least attentive 

 observers of the very couiinon cabbage-caterpillar 

 {Pontia BrassicfB)^ that when it ceases to feed, and 

 leaves its native cabbage to creep up walls and 

 palings, it is often transformed into a group of little 

 balls of silk, of a fine texture and a beautiful canary 

 yellow colour; from each of which there issues, in 

 process of time, a small four-winged fly (Micro- 

 gaster gloineratus, Spinola), of a black colour, ex- 

 cept the legs, which are yellow. By breeding these 

 flies in a state of confinement, and introducing them 

 to some cabbage-caterpillars, their proceedings in de- 

 positing tlieir eggs may be observed. We have more 

 than once seen one of these little flies select a cater- 

 pillar, and perch upon its back, holding her ovipositor 

 ready brandished to plunge between the rings which 

 she seems to prefer. When she has thus begun 

 laying her eggs, she does not readily take alarm ; 

 but, as Reaumur justly remarks, will permit an ob- 

 server to approach her with a magnifying glass of a 

 very short locus. Having deposited one egg, she 

 withdraws her ovipositor, and again plunges it with 

 another egg into a different part of the body of the 

 caterpillar, till she has laid in all about thirty eggs. 

 It is not a little remarkable, that the poor caterpillar, 

 whose body is thus pierced with so many wounds, 

 seems to bear it very patiently, and does not turn 

 upon the fly, as he would be certain to do upon 

 anotiier caterpillar should it venture to pinch him; 

 a circumstance by no means unusual. Sometimes, 

 indeed, he gives a slight jerk, but the fly does not 

 appear to be at all incommoded by the intimation 

 that her presence is disagreeable. 



The eggs, it may be remarked, are thrust suffi- 

 ciently deep to prevent their being thrown off when 

 the cateipillar casts its skin ; and, being in due time 

 hatched, the grubs feed in concert on the living 

 body of the caterpillar. The most wonderful circuUi- 



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