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TEXTBOOK OF ZOOLOGY 



the host to furnish them with food already digested and ready for 

 absorption. On the other hand, most endoparasites have their re- 

 productive organs enormously developed, sometimes so much so 

 that 90 per cent of the body is taken up by the reproductive sj^stem. 

 This is in keeping with the general rule that animals whose offspring 





C. 





//, 



D. 



E. 



Fig. 384. — Arthropod parasites. A, human itch mite, female, Sarcoptes scabiei, 

 ventral surface; B, ventral surface of male itch mite; C, body louse (cootie), 

 Pediculus humanus corporis; D, head louse, P, humanus capitis; E, crab louse. 

 Phthirius pubis. (From Sutton, Diseases of the Skin, published by The C. V. 

 Mosby Company.) 



have the least chance to survive usually produce the largest number 

 of offspring. In the ease of a tapeworm, for instance, the chance 

 of any one egg being eaten by the right kind of host, so that it can 

 develop into another tapeworm, is only one in a million, and tape- 



