204 THE SPOROZOA 



Leg., from the gut of Audouinia sp. Genus 70. Selenidium, Giard, 1884, 

 emend. Caullery et Mesnil, 1899, incl. Esarhdbdina, Mingazzini, 1891, 

 Polyrhabdina, Ming., 1891, and Platycystis, Leger, 1892. Body attenuated, 

 vermiform, without septum, showing longitudinal striations due to myocyte 

 fibrillae at the surface. Epimerite slender, conical, or large and globular 

 (Fig. 46, a, 6). Spores spherical, spined, and exceptional amongst Greg- 

 arines in being tetrazoic (Fig. 46, e, f). Parasites of Polychaetes. Type S. 

 pendula, Giard, from the body-cavity of Nerine ; S. echinatum, C. et M., 

 from the gut of Dodecaceria concharum ; other species from Scololepis fuli- 

 ginosa, Cirrhatuhis cirratus, and other marine Annelids. See especially 

 Caullery and Mesnil [86], 



ORDER 2. Coccidiidea 



The Coccidiidea are an order of the Telosporidia (p. 166), 

 characterised by the following distinctive features. They are cell- 

 parasites, attacking tissue - cells, and especially epithelial cells, 

 rarely other forms of tissue, and never blood-cells. The trophozoite 

 grows within the infected cell into an oval or spherical body, with 

 great resemblance to an ovum ; it is quite motionless, never at 

 any period amoeboid, and remains intracellular during at least the 

 whole trophic stage. The dissemination of the parasite is always 

 accomplished by means of resistent oocysts, the formation of which 

 is preceded by the conjugation of differentiated gametes in all cases 

 that have been thoroughly investigated. Within the oocyst the 

 zygote breaks up into sporoblasts (archispwes), which either become 

 converted into naked sporozoites (gymnospores), or into spores 

 (chlamydospwes), each containing from one to four sporozoites, 

 seldom more. In addition to this exogenous method of reproduc- 

 tion, or sporogony, by means of durable cysts, the life-cycle is often 

 complicated by endogenous multiplication, or schizogony, serving for 

 the increase of the parasites within the host. The schizogony is 

 not preceded by conjugation, and is not accompanied by formation 

 of any oocysts or sporocysts. 



The Coccidia have attracted the attention of naturalists and medical 

 men for a long time past, by their frequent occurrence in the rabbit and 

 other Vertebrates, in which they may be present in such masses that their 

 presence cannot fail to be detected by simple inspection when the host is 

 dissected. Earlier observers often held, however, very erroneous views 

 as to the nature of these parasites. Hake, who in 1839 was the first to 

 describe Coccidia, regarded them as pathological products of the diseased 

 animal in fact, as a form of pus -corpuscles ; and similar views were 

 held by many subsequent writers. On the other hand, a number of 

 authorities in the forties and fifties believed Coccidia to be eggs of 

 parasitic worms. Remak, in 1845, was the first to point out their 

 relations to Muller's " psorosperms," and in 1854 Lieberkiihn insisted 



