Chapter 25 

 Order 2 Coccidia Leuckart 



THE Coccidia show a wide zoological distribution, attacking 

 all vertebrates and higher invertebrates alike. The majority 

 are parasites of the epithelium of the digestive tract and its asso- 

 ciated glands. Asexual reproduction is by schizogony and sexual 

 reproduction by anisogamy in the majority of species. Both kinds 

 of reproduction take place in one and the same host body, with 

 the exception of such forms as Aggregata in which alternation of 

 generations and of hosts occurs. Taxonomy (Leger, 1911). 



Gametocytes similar; independent; a microgametocyte developing into 

 many microgametes Suborder 1 Eimeridea 



Gametocytes dissimilar; association begins during the late trophic life; 

 a few microgametes Suborder 2 Adeleidea (p. 590) 



Suborder 1 Eimeridia Leger 



These coccidians are, as a rule, intracellular parasites of the gut 

 epithelium. Both asexual (schizogonic) and sexual (sporogonic) 

 generations occur in one host, although in some there is also alter- 

 nation of hosts. The life-cycle of Eimeria schubergi, a gut parasite 

 of the centipede, Lithobius forficatus, as observed by Schaudinn, 

 is as follows (Fig. 243). The infection begins when the mature 

 oocysts of the coccidian gain entrance into the host through the 

 mouth. The sporozoites escape from the spores and make their way 

 through the micropyle of the oocyst into the gut lumen (p). By 

 active movement they reach and enter the epithelial cells (a). 

 These schizonts grow into large rounded bodies and their nuclei 

 multiply in number. The newly formed nuclei move to the body 

 surface, and each becomes surrounded by a small mass of cyto- 

 plasm, forming a merozoite. When the host cells rupture, the mero- 

 zoites are set free in the gut lumen, make their way into new host 

 cells and repeat the development (6). Instead of growing into 

 schizonts, some merozoites transform themselves into macro- or 

 micro-gametocytes (c). Each macrogametocyte contains retrac- 

 tile bodies, and becomes a mature macrogamete, after extruding 

 a part of its nuclear material (d, e). In the microgametocyte, the 

 nucleus divides several times and each division-product assumes 

 a compact appearance (f-h). The biflagellate comma-shaped mi- 

 crogametes thus produced, show activity when freed from the 

 host cells (i). A microgamete and a macrogamete unite to form a 

 zygote which secretes a membrane around itself (j). This stage is 



570 



