P.VC!v\RD.] 



nsTSECTS OF THE GARDElNr. 



15 



crust ill its place. Now there are two conditions to be ful- 

 filled in this act of parasitism ; for the insect preyed upon 

 must maintain its hold upon life, feeble as it may be, long 

 enough to enable the enemy lurking within, to build up its 

 tissues and add to its own strength by daily depleting from 



Fig. 4. 



Ichneumon (Muerocentrus). 



the stores of vitalized food about it ; and on the other hand 

 the parasite must carefully avoid touching the vital parts of 

 its host. It must content itself with feeding upon the fatty 

 portions alone of the body. 



That family of the Hymenoptera of which the ichneu- 

 mon-fly (Fig. 4) is a type, and many species of true flies 



15 



