158 THE PROTOZOA 



Coccidiida followed that of Leuckart ('79) in the case of Coccidium 

 oviformis, a parasite of the rabbit. According to this view, the 

 adult Coccidium, which consists of a globular or oval mononucleate 

 parasite, living in the epithelial cells of the digestive tract and the 

 related organs, encysts and falls into the lumen of the digestive 

 tract, from which it is defecated with the faeces. Inside of the cyst 

 the plasm divides into several parts (in Coccidium four), and these 

 parts, after the formation of a firm, resisting membrane, form the 

 permanent spores. Each spore divides into two parts in Coccidium, 

 and these two parts constitute the end product of reproduction, 

 according to the older view. Each of the parts forms a germ or 

 sporozoite, which penetrates a new cell-host and develops again to 

 the adult organism. 



This cycle, while perfectly logical, left unexplained the immense 

 multitudes of parasites found in the epithelial cells of every 

 Cocciditim-mfected rabbit. The first attempt to explain its wide 

 distribution was made by R. Pfeiffer ('92), who insisted that, in 

 addition to this exogenous spore-formation, there exists an internal 

 reproduction as well, which leads to further infection in the same 

 host, or, as he called it, to auto-infection. In contrast with the first 

 method, this was called the endogenous sporozoite-formation. This 

 view was based upon the discovery by Pfeiffer of spore-forming cells 

 in the tissues of the host, in addition to those in the lumen of the 

 digestive tract. The majority of investigators along this line have 

 accepted the latter view. There are two notable exceptions, how- 

 ever, one of whom is Labbe, who holds that these smaller forms are 

 only poorly fed individuals and not sporozoites, and explains the 

 undeniable auto-infection through simple division of the parasites. 



A large number of papers soon followed, some on Coccidium, others 

 on related forms. Mingazzini ( '92) followed out the multiple division 

 of the nucleus in the formation of the endogenous sporozoites. 

 Podwyssozki ('94) made the discovery that there are two kinds of 

 these endogenous forms, which were accordingly named microsporo- 

 zoites and macrosporozoites. It was Schuberg ('95), however, who 

 first suggested, although he did not confirm the suggestion, that 

 these two forms of sporozoites conjugate and thus lead to sexual 

 reproduction. Labbe strongly opposed the latter view, and held that 

 the larger types of supposed dimorphic spores belong to some un- 

 known species of Coccidiida, and that the smaller forms are degen- 

 eration types. 



The way was thus prepared for the discovery of conjugation among 

 the cells of the Coccidiida, a discovery made first by Schaudinn and 

 Siedlecki ('97). In two different species, Coccidium Sclmeidcri and 

 Adelea ovata, it was found that a large cell, an egg, is fertilized by a 



