32 DISEASES OF CROPS. 



blue fore-wings marked with several roimdisli, bright-red 

 spots." The larva (caterpillar) feeds upon the leaves o£ 

 trefoil and various herbaceous plants. 



(6) The Parasites of Vetches or Tares 



{Vicia sativa). 



The parasites of this crop are similar to those of the 



pea. Peronospora vicice, already described under the 



name of the " pea mould," attacks Vicia sativa as well as 



other plants. 



So far we have surveyed the life-histories of the prin- 

 cipal parasites which injure leguminous crops. To con- 

 clude this part of the subject we quote from Professor 

 P. J. Van Beneden's Animal Parasites and Messmates 

 (English edition, p. 85) : " The parasite is he whose pro- 

 fession it is to live at the expense of his neighbour, and 

 whose only employment consists in taking advantage of 

 him, but prudently, so as not to endanger his Hfe. He is 

 a pauper who needs help, lest he should die on the public 

 highway ; but who practises the precept — not to kill the 

 fowl in order to get the eggs. . . . The beast of prey 

 kills its victim in order to feed upon his flesh, the para- 

 site does not kill ; on the contrary, he profits by all the 

 advantages enjoyed by the host on whom he thrusts his 

 presence." 



