FACTS Ar.di r \vi:i,i, knuwn am.maf.s. 



Hil 



wliirli ltor(' holts into lliu bodies ol" cuws, slicep, aii<l other 

 lu'rbivorous aiiinuils, and tlicri'iii deposit eggs; that those 

 eggs luituli into li/.ards ; that these li/.anis grow fat at tlie 

 exi)ense of the sheep, but without ininiediately killing them; 

 that, in faet, a sheep so affected could live without eating for 

 years, where otherwise it wouhl die in a few days without 

 tbod ; that the li/.ards in time leave the body of the sheci)in 

 nundjcrs and Imii'ow into the ground: and that, linally, 

 after the lapse of an indi'tinite })eriod, they issue forth in 

 tile Ibrm of birds like their parents, wh}-, not one of you 

 would believe nio ! But, it is only by drawing some such 

 striking picture that I can hope to convey to you any cor- 

 rect iilea of the remarkable facts of parasitism in the insect 

 world. Most insects have primary parasites, but in some 

 eases these are themselves prej'ed on by secondary parasites 

 and these again by tertiary ones ; so that a worm may be a 

 })eripatetic banqueting hall for several other insects at the 

 same time. 



To be more explicit and exact, let us take a familiar ex- 

 ample. The typical female Ichneumon-fly has something 



Fig. 12. — Pinipla annulipis : Outline side view of female .ami of male abdo- 

 men. (After Riley. ) 



of tins form which I will draw on the blackboard, (see 

 Fig. 12, Pimpla annnlipis Br.,) its chief charticteristics be- 

 ing the long ovipositor with the two sheath.s, }>ossessed by 

 the female but not by the male. 



