422 



THE PROTOZOA 



Analogy with other Ncosporidia would lead us to identify this with the 

 planont- phase, initiated, possibly, by sexual processes between different 

 amcebulse and subsequent active multiplication. The second period of 

 the development begins with the penetration of the amoebula into a 

 muscle-fibre, in which the parasite grows into a Miescher's tube and forms- 

 spores. 



, The intramuscular development of the parasite begins by multiplication 

 of the nuclei to about twelve, forming a plasmodium (Fig. 176, A). This next 

 becomes divided up, in parasites about thirty-three days old, into separate cells, 



pansporo blasts or sporonts, whichmultiply 

 actively by division. The form of the para- 

 site now becomes elongated ; this stage 

 is reached in from forty-eight to sixty 

 clays (Fig. 176, B). At this point the para- 

 site may disintegrate, setting free the 

 sporonts, or may develop into a Miescher's 

 tube. In the first case the sporonts 

 wander out and establish themselves in 

 other muscle-fibres, where each sporont 

 initiates a fresh development, thus spread- 

 ing the infection in the tissues of the host. 

 In the second case a membrane is secreted 

 round the body, which forms the striated 

 envelope prolonged inwards to form the 

 chambers. The striated envelope of the 

 Miescher's tube has generally been com- 

 pared to the striated ectoplasm of some 

 Myxosporidia e.g., Myxidium lieber- 

 killmi ; but according to Fiebiger it is 

 not ectoplasm, but altered muscular 

 tissue. The nuclei of the muscle-fibres 

 are stimulated by the parasite to multi- 

 plication and migration. The body then 

 consists of a peripheral zone of sporonts, 

 multiplying actively, and a central 

 region in which spores are differentiated. 

 In the development of the spore, the 

 sporont becomes sausage-shaped, and 

 multiplies l>y division. Finally the 

 sausage-shaped bodies become spores, 

 and are stated to be at first binucleate ; 

 probably one nucleus is that of the 

 amoebula, the other that of the capsu- 

 logenous cell, parietal cells being absent ; 

 but these statements are at present hypo- 

 thetical and require substantiation. FuDy- 

 formed spores are found in parasites 

 eighty to ninety days after the infection 

 of the host. 



In old infections the parasites may have 

 destroyed the muscle-fibre completely, 

 so that the Miescher's tube lies in the 

 connective tissue. In such forms the 



centre of the body may consist of granular debris, derived from the 

 disintegration of spores which are past their prime and have degenerated. 



B 



1'iG. 176. Four stages in the de- 

 velopment of a " Miescher's tube " 

 of Sarcocystis muris in the pectoral 

 muscles of white rats infected ex- 

 perimentally. A, Parasite 25 fj. in 

 length, fifty days after infection ; 

 the contents of the body beginning 

 to divide into separate cells ; 11, 

 parasite of the same age, 35 fj, in 

 length, division of the contents 

 further advanced ; C, parasite of 

 the same age, 60 /* in length, con- 

 taining separate cells ; at the 

 centre the division of a sporont 

 into two sickle-shaped bodies is 

 seen to be taking place ; D, middle 

 portion of a tube about 450 /J. 

 in length, seventy days after in- 

 fection, showing two couples 

 of sickle-shaped bodies formed 

 by division of a sporont. After 

 Negri. 



So far as it is possible to draw conclusions in the present state 

 of knowledge, the Sarcosporidia would appear to be true Cnido- 

 sporidia, with spores which contain each a single polar capsule, 



