352 THE PROTOZOA 



itself by a tough oocyst (Fig. 155, 0) ; in this stage it is expelled from the 

 body with the faeces. The subsequent development of the oocyst, spore- 

 formation, etc., are not known. 



From these data it is sufficiently clear that Selenococcidium is perfectly 

 gregarine-like in its trophic phase and in its schizogony ; the trophozoites are 

 free vermicules which multiply just as in Schizocystis. The parasite only 

 penetrates into a cell when it enters upon reproductive phases. On the other 

 hand, the sporogony, so far as it is known, and especially the sexual processes, 

 are entirely coccidian in type. Selenococcidium links the gregarines and 

 coccidia in a striking and convincing manner, as will be discussed further 

 below. 



Classification. The Coccidia have been classified in various ways at different 

 times, as increased knowledge of these organisms has shown older schemes 

 to be artificial or unnatural. The following classification is in the main that 

 of Liihe (392), with certain modifications. Some genera have not, however, 

 been investigated sufficiently to make their systematic position certain. 



Suborder I. : Prococcidia. 



Trophozoites free, vermiform, motile ; schizogony similar in type to that 

 of Schizogregarines. The only genus known at present is Selenococcidium. 

 The genus Siedleckia should perhaps be placed here, perhaps in the Schizo- 

 gregarines near Schizocystis ; its sporogony is as yet unknown. 



Suborder II. : Eucoccidia. 



Trophozoites typically -intracellular, motionless, oviform, rarely free or 

 vermiform ; schizogony of coccidian type. 



SECTION A. Forms in which the sporonts do not associate prior to gamete- 

 formation, and numerous microgametes are produced : 



Family 1 : Coccidiidce (Eimeridce). The schizogony is of a simple type, 

 as described in C. schubergi. Examples : Coccidium (Eimeria) and allied 

 genera ; Barroussia (Barrouxia), with type B. ornata, from the gut of Nepa 

 cinerea ; Cydospora, including C. caryolytica, from the intestine of the mole ; 

 and other genera. Cryptosporidium muris, from the gastric glands of the 

 mouse, has free trophozoites and produces a single tetrazoic spore. 



Family 2 : Carvotrophidce. With double multiple fission in the schizogony. 

 Example : Caryotropha mesnilii, parasite of the Annelid Polymnia nebulosa 

 (Siedlecki, 653). Klossiella muris,* from the kidney of the mouse, should 

 perhaps be referred to this family, possibly also Merocystis kathce (Dakin). 



SECTION B. Forms in which the sporonts (gametocytes) associate prior 

 to gamete -format ion, and the number of male gametes is reduced to four : 



Family 3 : Adeleidce. With sporocysts. Examples : Adelea, with several 

 species, of which the best known is A. ovata, parasite of the intestine of 

 Lithobius ; Klossia, with type K. helicina, from the kidneys of Helix spp. ; 

 Orcheobius herpobdellce, from the testis of the leech Herpobdella (Kunze) ; 

 and Caryospora simplex, from the intestine of Vipera aspis, in which the 

 contents of the oocyst form a single octozoic spore (Leger, 644). Minchinia 

 chitonis, from the liver of Chiton and Patella spp., should perhaps be referred 

 to this family, but the gamete-formation is not yet known. 



Family 4 : Legerellidce. Without sporocysts. Example : Legerella nova, 

 parasite of the Malpighian tubes of Glomeris. 



A classification similar in the main to the above has been put forward by 

 Leger (644), who terms Section A the Eimeridea. Section B the Adeleidea. 



* My friend Dr. A. C. Stevenson, of the Pathological Department, University 

 College, who has studied Klossietta, informs me that he considers it possible that 

 it may represent a stage of Hoemogr&jarina musculi (p.JJ77). 



