420 THE PROTOZOA 



structure of the spores is still a matter of dispute, and it is 

 possible that there is more than one kind of spore even in the 

 same species of parasite. A remarkable feature of the spores 

 in some species, at least is that they are motile when set free : 

 for example, in S. muris. They are also extremely delicate 

 structures, easily injured by external media, in marked contrast to 

 the spores of the other orders of Cnidosporidia. The spores of 

 8. muris, S. bertrami (of the horse), and $. tenella, reproduce them- 

 selves by division (Negri, Fiebiger, Teichmann). Finally it must 

 be mentioned that the spores of Sarcosporidia contain a true toxin, 

 which was named by Laveraii and Mesiiil " sarcocystine." Its 

 properties have been investigated recently by Teichmann (25) and 

 Teichmann and Braun (26). 



The natural mode of transmission of the Sarcosporidia remains 

 to be discovered. It was found by Theobald Smith that mice could 

 be infected experimentally with S. muris by feeding them with the 

 flesh of other infected mice ; but it is extremely unlikely that 

 cannibalism is the method whereby sheep and other ruminants 

 become infected with these parasites. All experiments indicate 

 that the spores germinate in the digestive tract of the new host ; 

 but the delicate nature of the spores seems to preclude any possi- 

 bility of the occurrence of ordinary contaminative infection, as in 

 other Cnidosporidia. In this connection attention should be drawn 

 to the statement of Watson, that the spores are to be found in the 

 circulating blood, indicating the possibility of transmission by an 

 intermediate host. 



In spite of several recent investigations upon the structure and develop- 

 ment of the Sarcosporidia, the subject is in a confused state, even the structure 

 of the spores being still disputed. It is therefore difficult to obtain a clear 

 notion of the course of the life-cycle in these organisms. 



According to Laveran and Mesnil, the spores of S. tenella (Fig. 175) are 

 sausage-shaped bodies, curved, with one end more pointed than the other. 

 At the pointed end is a striated structure representing a polar capsule, and 

 at the blunt end is a nucleus, while the middle of the body is occupied by 

 coarse, deeply-staining, metachromatinic grains. Watson also figures a large 

 nucleus near the blunt end of the spore, and places the polar capsule at the 

 pointed end. Negri also describes the spores of S. muris and S. bertrami as 

 having the nucleus near tha blunt end, while the opposite extremity appears 

 hyaline and homogeneous for a certain distance. Betegh, again, describes 

 a nucleus at the blunt end of the spore, and one or two " centrosomes " in the 

 middle region. Erdmann (790), on the other hand, places the nucleus in the 

 middle of the body amongst the metachromatinic grains, and describes it as 

 consisting of a large dense karyosome lodged in a small vacuole ; she does not 

 seem to be decided, however, whether the polar capsule is at the pointed or 

 the blunt end of the spore. Teichmann describes a large nucleus at the 

 blunt end of the body, and is doubtful as to the existence of a polar capsule. 

 So far as it is possible to draw any conclusions from so many contradictory 

 statements, the clear description given by Laveran and Mesnil seems to be, 

 on the whole, confirmed. But according to Crawley, the spores of 8. rileyi 

 are binucleate; compare those of Gastrocystis (Fig. 179, p. 428). It is not 



