COCCIDIANS 



171 



host cell which has been preyed upon and destroyed, invade fresh 

 cells, multiply again, and thus eventually destroy large portions 

 of the lining of the digestive tract. The daughter coccidians 

 are not adapted for withstanding conditions outside the intestine 



In intestine. 



V |\j Outside body.^ 



M 



FIG. 48. Life history of Eimeria avium. A, infection of epithelial cells of in- 

 testine by sporozoites ingested with food or water; B, growth inside cell; C and D, 

 sporulation and formation of young spores; E and G, formation of female gamete; 

 F and H, formation of male gametes; /, fertilization; /, fully developed oocyst as 

 passed out with faeces; K, L and M, formation of four sporocysts; N, complete 

 development of sporocysts, each containing two sporozoites; O, same, ingested by 

 susceptible animal; P, sporocyst liberated from oocyst in alimentary canal; Q, 

 liberated sporozoite ready to infect epithelial cell, as shown in A. 



of the host, and therefore the parasite would be exterminated 

 with the death of its host were it not protected in some manner 

 against this calamity. The sexual phase of its life history serves 



