208 THE SPOROZOA 



respect the predilections of Coccidia are the opposite of those of 

 Myxosporidia, which frequently attack the ovary but never the testis. 

 A given species of Coccidian parasite may confine its attentions 

 entirely to some particular organ, or it may attack several organs, 

 as for example Coccidium minutum, Thel., found in the liver, spleen, 

 and kidney of the tench; but as a rule it is rare for a form 

 infesting the epithelium of the digestive tract to attack other 

 internal organs as well. 



Coccidia during the trophic stage are always intracellular 

 parasites, 1 and each trophozoite destroys completely the cell which 

 harbours it. As a rule the trophozoite lies in the cytoplasm and 

 does not attack the nucleus directly, but pushes it to one side, often 

 indenting or compressing it. The first effect of the extranuclear 

 parasite is to produce a considerable hypertrophy of the host-cell, 

 especially of its nucleus. The cell is stimulated to increased 

 metabolism, shown not only in rapid growth, but also in the 

 formation, by it of fatty substances, which serve as nutriment 

 for the parasite and are consumed by it (Schaudinn [51]). The 

 effects of the parasite are not confined to the cell which harbours 

 it, but may extend to the surrounding tissues ; in Helix hortensis 

 attacked by Klossia helicina the neighbouring epithelial cells of the 

 kidney are stimulated to karyokinesis and multiplication, and a 

 proliferation of the cells of the connective tissue is induced, leading 

 to the formation of a fibrous envelope round the masses of Coccidia 

 as a healing process on the part of the host (Laveran [38]). 

 Ultimately, however, the infected cell is so weakened that it can 

 no longer assimilate, but dies and is finally absorbed by the 

 parasite, only a compact lump of chromatin and a small quantity 

 of protoplasm remaining. The parasite then passes into the 

 reproductive stage, either still enclosed by the remnants of the 

 cell it has destroyed, in schizogony, or freed from the cell, in 

 sporogony. 



A certain number of Coccidia occur, on the other hand, as 

 intranuclear parasites. The schizogonous generations of certain 

 species of Coccidium occurring in Amphibia (frog, salamander, newt) 

 commonly attack the nucleus itself of the infected cell, and have 

 hence been described by Steinhaus under the generic name Karyo- 

 phagus. The recently described Cyclospora caryolytica, Schaud., 

 parasite of the intestinal epithelium of the mole, owes its specific 

 name also to its intranuclear habitat, which in this case seems to 

 be an invariable characteristic of the parasite. The effects of this 

 intranuclear parasitism have recently been studied by Schaudinn 

 [5 la] and Dormoy [33], and are seen chiefly in an enlargement of 



1 Very recently Laveran and Mesnil have described a species under the name 

 Coccidium mitrarium (see p. 233), which, according to these authors, is unique 

 amongst Coccidia in having an extracellular development like a Gregarine. 



