2 SPOROZOA. 



Eimeria and Isospora. Pfeiffer (1892) was the first to describe 

 the theory of alternate generations, and Schaudinn and 

 Siedlecki (1897) showed that there are two kinds of gametes 

 in Goccidium, and that the macro- and microgametes conjugate 

 to form zygotes. Later (1898) Siedlecki pubHshed an account 

 of the sexual cycle of the Coccidian Aggregata, and in 1899 

 gave a detailed account of the entire ]ife-history of Adelea. 

 This series of classical researches led up to the pubHcation of 

 the description of the complete hfe- cycle of Goccidium schubergi 

 by Schaudinn (1900). 



The H^MOSPOEiDiA, or blood-inhabiting Sporozoa, were 

 discovered as late as the eighties of the last century. Laveran 

 observed the malarial parasites in the human blood in 1880, 

 and pubhshed a description in the following year. He observed 

 the amoeboid, rosette, sphere, crescent and the flagellate stages, 

 but did not determine the relationship of the various stages, 

 nor did he recognize the animal nature of the parasites. The 

 genus Plasmodium was instituted by Marchiafava and Celh 

 (1895). Further discoveries leading to the elucidation of the 

 complete hfe-cycle of the malarial parasites were made by 

 Metchnikoff (1887), Golgi (1889), Danilewsky (1891), Manson 

 (1894, 1896), MacCallum (1897, 1898), Ross (1898, 1899), 

 Grassi (1898), and others, and will be referred to elsewhere in 

 this volume. Smith and Kilborne (1893) demonstrated that 

 Babesia, the cause of Texas fever of cattle, was transmitted 

 from host to host by ticks, and were thus the first to show the 

 important part played by insects in the transmission of para- 

 sitic Protozoa. 



We owe the term Sporozoa to Leuckart (1879), who intro- 

 duced it to include the Gregarinida and the Coccidia. The 

 H^MOSPORiDiA were included later, when the study of the 

 complete hfe-cycle showed the close resemblance of various 

 stages with those of the Coccidia. Besides these three well 

 recognized groups, there are other groups of parasites, found 

 in Fishes, Arthropods, etc., which, on account of their forming 

 spores, came to be included in the Sporozoa. In a large 

 majority of these, known as the Cnidosporidia, the spore 

 contains a coiled filament inside a polar capsule. Schaudinn 

 (1900) divided the Sporozoa into two subclasses — (i) the 

 Telosporidia, to include the Gregarinida, Coccidia, and 

 H^MOSPORiDiA ; and (ii) the Neosporidia, to include the 

 Cnidosporidia, Sarcosporidia, and Haplosporidia. The 

 members of both these subclasses produce resistant spores, 

 but according to many authors the affinities between the two 

 are not sufficiently close to justify their inclusion in the same 

 class. Hartmann (1907) estabHshed two classes, for which 

 he employed Schaudinn's names — Telosporidia and Neo- 

 sporidia. Later, Prowazek and JoUos (1922) and Hartmann 



