ECOLOGY, C0MMENSAL1SM AND PARASITISM 



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the most instructive scheme for illustrating the stages in the life 

 history and the adopted terminology. 



Eimeria schubergi is a common parasite of the centipede's intestine, 

 infection being brought about by contaminated food. In such food 

 substance the germs of Eimeria are protected against drying and 

 other adverse external conditions by cyst membranes, one of which, 



Fig. 173. — Eimeria Schubergi. Sporozoites penetrate epithelial cells and grow 

 into adult intracellular parasites (a). When mature, the nucleus divides repeatedly 

 (6), and each of its subdivisions becomes the nucleus of an agamete (c). These enter 

 new epithelial cells and the cycle is repeated many times. After five or six days of 

 incubation, the agametes develop into gamonts; some are large and stored with yolk 

 material (d, e, /), others have nuclei which fragment into chromidia which become 

 the nuclei of microgametes (d, h, i, j). A macrogamete is fertilized by one micro- 

 gamete (g) and the zygote forms an oocyst (k) . This forms four sporoblasts, each 

 with two sporozoites (/). (After Schaudinn.) 



the sporocyst membrane, encloses 2 germs termed sporozoites. 

 The second and outer membrane— oocyst— encloses a group of 4 

 sporocysts (Fig. 173) and 8 sporozoites. 



Under the action of digestive fluids the double membrane about 

 the sporozoites are opened and the germs arc liberated. They make 

 their way to glandular cells of the intestine and get into the cyto- 

 plasm, usually 1 to a cell (Fig. 173, a). In the cytoplasm the sporo- 



