760 SARCOSPORIDIA 



recognizes a sixth genus, Neoactinomyxon, has recently published a 

 memoir on the morphology, development, and systematics of the 

 group. 



PARASITES OF UNDETERMINED POSITION. 



There are a number of organisms which are usually grouped with the 

 Cnidosporidia, though they do not show any of their main characters. 

 It is doubtful if some of them are Protozoa at all. The chief of these are 

 the Sarcosporidia, which are parasitic in the muscle fibres of vertebrates, 

 and have the form of elongate chambered bodies filled with sickle-shaped 

 spores; the closely related Globidium (cysts of Gilruth), which give rise to 

 nodules in the mucosa of the stomach and intestine of ruminants and 

 other animals; the Haplosporidia, which occur chiefly in invertebrates 

 in the form of uninucleate or multinucleate cytoplasmic bodies and 

 resistant spores; and the Serumsporidia, which are found in the body- 

 cavity fluids of aquatic Crustacea and larvae as small round cells which 

 multiply by binary fission or schizogony. The Rhinosporidia, which 

 produce nasal polypi, have been usually classed with the Haplosporidia, 

 but Ashworth (1923) has shown conclusively that they are fungi, and 

 not Protozoa, and this appears to be true of Globidium and possibly the 

 Sarcosporidia. 



Sarcosporidia Biitschli, 1882. 



The parasites included under this heading are regarded as belonging to 

 the genus Sarcocystis Ray Lankester, 1882, and are usually classed with 

 the Cnidosporidia; but, as noted above (p. 717), there are no adequate 

 grounds for this. They are often grouped as a separate order, Sarco- 

 sporidia Biitschli, 1882. They are found chiefly as parasites of the striated 

 muscle fibres, and less frequently of the unstriated fibres of mammals; but 

 a few forms have been recorded from birds and reptiles. 



They have been found occasionally in man, and are very common in 

 sheep, cattle, and horses. A form which occurs in mice and rats has been 

 studied more than others on account of the fact that experimental infec- 

 tions can be produced by feeding the animals on infected tissues. 



Morphology. — In whatever hosts they occur, the parasites are very uniform 

 in appearance, though the forms described vary considerably in size. 

 Since the discovery by Miescher (1843) of a form in muscle fibres of mice, 

 they have frequently been known as " Miescher's tubes," and the spores 

 as " Rainey's corpuscles." They are sometimes so small that they can 

 only be detected with the microscope. At other times they are seen as 

 tiny white streaks in the muscle fibres, while they may be as much as 

 5 centimetres in length. When seen entire after removal from the tissues, 



