COCCIDIUM 127 



zygote becomes surrounded with a thin pelUcle, becomes 

 pointed at both ends, and works its way into the m.osquito's 

 gut wall, where it burrows through the lining and comes 

 to rest, developing a globular envelope or oocyst. Great 

 growth now takes place, both of oocyst and contents. 

 Ultimately there are formed within the oocyst an enormous 

 number of elongated sporozoites. The oocyst then 

 bursts, and the sporozoites are set free in the mosquito's 

 blood spaces. Very many of them accumulate in the 

 salivary glands, and are passed out with the salivary juice 

 to start the life-cycle anew. 



Ninth Type of Protozoa — Coccidium schubergi 



Reference may here be made to the common Coccidia, 

 intracellular Sporozoa, attacking mainly the epithelial 

 cells of the gut or associated organs. They are found 

 chiefly in insects, myriopods, molluscs, and vertebrates. 

 Thus Coccidium schubergi infests the intestinal epithelium of 

 the centipede Lithobius forficatus. The adult is a minute 

 oval or spherical cell with a nucleus. It lives a quiescent 

 life within the host cell, growing and absorbing nourish- 

 ment until the resources of the cell are exhausted. 



Life-history. — The coccidium enters the host cell as a 

 minute sickle-shaped body, pointed at the anterior end, and 

 more blunt posteriorly. This is the sporozoite stage of the 

 life-history ; it is liberated from a cyst (oocyst) when the 

 latter is swallowed by the centipede in its food. When 

 freed in the gut the sporozoite progresses by forward gliding 

 movements, alternating these by flexions, bending itself like 

 a bow and straightening out again. When about to enter 

 an epithelial cell it presses the anterior end through the cell 

 wall and wriggles its way in. Once within the cell in which 

 development is to proceed, its movements gradually cease, 

 but it may pass through several cells before coming to rest. 

 Within the host cell the coccidium — now in the trophozoite 

 stage — becomes oval in form, and in about twenty-four 

 hours has reached full size and has exhausted the host cell 

 contents. This is the completion of the trophozoite period, 

 and the parasite now enters the schizont stage, where its 

 nucleus divides into a number of daughter nuclei. These 



