GENKRAI. COXSIDKRATION OF DISICASI-:. 



69 



Fis- 40, — 0-\.vuris Ciirvula, after Nil^s, 



a. Adult worm, ;■. Caudal, 



b. (_'iphalic cxtri mitj'. 



sicollis inhabits the liver of the rat durinj^- its c\stic statue and 

 the intestine of the cat during- the adult stage. 



Helminthes produce injur^' to their host bv consuming food, 

 by sucking blood and by liberating injurious chemic substances. 



Arthropoda. 



This branch includes many parasitic representatives, as flies 

 and mosquitoes (diptera), fleas (siphonaptera) lice (hemip- 

 tera), itch mites and ticks (acarina). The entire order, siphon- 

 aptera and hemiptera, most of the order acarina, and manv rep- 

 resentatives of the order diptera are parasitic. Of the parasitic 

 arthropoda some are temporary and some are permanent para- 

 sites, and with one or two exceptions tliev are all external para- 

 sites. 



The structural peculiarities that differentiate arthropoda from 



