SPOROZOA 89 



Suborder COCCIDIA 



Coccidiomorpha, for the most part gut parasites ; of which the zygote 

 is non-locomotory ; the sporozoites are nearly always encased; and 

 the gamonts often form a syzygy. 



Eimeria (Fig. 74) is parasitic in the intestinal epithelium of various 

 vertebrates and invertebrates. E. schubergi, from the intestine of the 

 centipede Lithobtus, may be described as a type of the suborder. The 

 spherical trophozoite (agamont) undergoes schizogony (agamogony) 

 by multiple fission within the epithelial cell which it inhabits. The 

 spindle-shaped schizozoites (agametes) being set free into the cavity 

 of the organ, each infects another cell in which it grows like its parent. 

 After some days of this there occur fissions in which the young on 

 invading a host cell grow into adults unlike their parents and of two 

 kinds — male and female gamonts. Each female gamont extrudes 

 stainable matter from its nucleus and thus becomes a female holo- 

 gamete. In the male gamont the nucleus divides several times, and 

 the daughter nuclei are set free with portions of the cytoplasm as 

 biflagellate male gametes, which are thus merogametes. The gametes 

 leave the host cell and unite while free in the gut cavity. The zygote 

 nucleus undergoes what is probably a reduction division and encysts. 

 Within its cyst (the oocyst) it divides by multiple fission into four 

 sporoblasts each of which forms a cyst of its own (a secondary sporo- 

 cyst) in which it divides into two sporozoites. Thus sporogony takes 

 place in two stages. In each of these there is some residual proto- 

 plasm. Meanwhile the oocyst has passed out of the host in the faeces. 

 Infection of a new host takes place by contamination of food by the 

 encysted spores, which hatch in the intestine. 



Aggregata is remarkable among coccidians for having two hosts. 

 Its agamogony takes place in crabs and involves a generation of sporo- 

 blasts, but is not repeated. A cuttlefish, devouring a crab, ingests the 

 agametes, which in the new host proceed to become gamonts. After 

 gamogony with flagellate male gametes, fertilization, and sporogony, 

 the spores, containing four or more sporozoites, are passed with the 

 faeces of the mollusc and swallowed by a crab. 



Adelea is parasitic in the epithelium of the gut of Lithobius. Its life 

 history resembles that of Eimeria, but the gamonts, which differ con- 

 siderably in size, the male being the smaller, become free and form 

 a syzygy in the gut, though without encystment. The male gametes 

 are consequently not under the necessity of reaching the female by 

 swimming, and are not flagellated. 



Haemogregarina has become completely a blood parasite, and has 

 a life history closely resembling that of the Haemosporidia, with the 

 sexual process in an invertebrate host (see below). Since, however, it 



