SAECOSPORIDIA. 361 



III. Subclass SARCOSPOEIDIA 

 Biitschli, 1882. 



These are typically parasites of the muscles of mammals, 

 although birds and some reptiles are also known to harbom- 

 them. They usually affect the striped muscles of the skeleton, 

 tongue, larynx, and diaphragm. Lying between the muscle- 

 fibres are thin- walled, whitish, tubular cysts termed Miescher's 

 tubes, which are the remains of an infected muscle-fibre, 

 the membrane of which is distended over the sac containing 

 the parasites. They are generally visible to the naked eye, 

 and often very large. When examined microscopically each 

 is seen to consist of an envelope, from which partitions run 

 inward, dividing the interior into a number of chambers 

 containing vast numbers of crescent- shaped spores, the so-called 

 " Raitiey's corpuscles." The spore is rounded at one end and 

 pointed at the other ; it contains a nucleus near the rounded 

 end and a collection of deeply staining chromatinic grains 

 near the pointed end. Laveran and Mesnil described a striated 

 structure at the pointed end which several workers considered 

 as suggesting a rudimentary polar capsule, but recent authori- 

 ties do not regard it as such. 



The spores are taken into the digestive tract of a specific 

 host through the mouth. The spore -membrane ruptures, 

 setting free the sporozoite, which enters the gut-epithelium. 

 After multiplying there the organism makes its way into 

 the muscular tissue. At first there is an elongate multi- 

 nucleate mass, which may or may not divide into uninucleate 

 bodies and which become the centre of infection in other 

 muscle- fibres. Some of these trophozoites grow in size, and 

 the body becomes divided into chambers, inside which spores 

 are formed. 



Development has been studied chiefly in experimentally 

 infected mice by Erdmann (1910, 1914), Negri (1910), and 

 Crawley (1916), and in sheep by Alexeiefi" (1913). Smith 

 (1901, 1905) was the iirst to demonstrate that mice could be 

 infected by feeding them with the flesh of other infected 

 mice. Negri (1910) and Darhng (1910 a) showed that guinea- 

 pigs could be infected with the parasite of rats, and Darling 

 also pointed out that the forms in guinea-pigs are morpho- 

 logically identical with those from man. Erdmann (1910) 

 infected mice with the parasite of sheep. Wenyon (1926) 



