MORPHOLOGY AND TAXONOMY OF THE SPOROZOA 555 



The spores on the whole are less complex than those of the Myxo- 

 sporidia. They are small and ovoidal or bean-shape and rarely 

 (TelomyxahegeT and Hesse, 1910) with more than one polar capsule, 

 in some cases without any. The capsules and threads are invisible 

 or very difficult to see in the living spore (hence cryptocysts), but 

 are demonstrable upon treatment with alkalies. The spore capsule 

 is bivalved in some but consists of a single piece in other species. 

 The history of spore-formation agrees in the main with that of the 

 Myxosporidia but authorities disagree as to details and convincing 

 proof is yet to be demonstrated. Fertilization processes have been 

 described by Mercier (1908, 1909) whereby two isogametes of Thelo- 

 hania giardi fuse to form the pansporoblast. Autogamous union 

 of nuclei prior to spore formation and not, as in Myxosporidia, in 

 the later sporoplasm, has been described by Debaisieux (1913, 1915) 

 in species of Thelohania and Glugea. 



The life history of Stempellia magna as given by Kudo (1924) is 

 typical of the Microsporidia (Fig. 222). The polar filament of the 

 spore (S) is extruded when the spore reaches the mid-gut of its 

 culicine host; the uninucleate sporoplasm creeps out of the opening 

 made by the cast-off filament, enters a fat cell and becomes an 

 agamont and reproduces by division (J). The products ultimately 

 become multinucleated with from four to eight nuclei (B); the 

 organisms then breaking up into binucleated cells, the nuclei of which 

 fuse after discarding some chromatin (0). This is identified as a 

 sporont which may become transformed into a single spore (D), or 

 it may divide into two (E), four (F) or eight (G) sporoblasts, each 

 of which forms a single spore after chromidia formation and recon- 

 struction of small nuclei (H, I), some of which take part in the 

 formation of the capsular thread. A more simple life history is 

 shown by Thelohania legeri according to Kudo (Fig. 223). 



Class III. ACNIDOSPORIDIA Cepede. 



The Sarcosporidia are parasites of vertebrates, particularly mam- 

 mals, in which the ultimate seat of parasitism is the muscular tissue. 

 There is but one genus — Sarcocystis— with several species in pigs 

 (S. miescheriaria Kiihn, 1S65, forming "Miescher's tubules"), in 

 sheep (S. tenella Railliet, 1886), in cattle (S. blanchardi Doflein, 

 1901), in mice (S. muris Blanchard, 1885), in opossums (S. darlingi 

 Brumpt, 1913), in monkeys (S. kortei Castellani and Chalmers, 

 1909) and in man (S. lindemanni Rivolta, 1878). A species from 

 birds was described by Stiles (1893) under the name of S. rileyi. 



Sarcosporidia have been studied by a host of observers and an 

 almost equal number of interpretations has been the result. The 

 best-known species is S. maris from the mouse in which, beginning 

 with Th. Smith's (1901) inoculation experiments by feeding infected 



