1911.] NATURAL SCIENCES OF PHILADELPHIA. 461 



was also indicated by the fact that where the shell was thin, it was 

 quite dense, and where thick, very loose and open. The distortion 

 was probably due to exigencies of fixation, but, as already indicated, 

 the cysts must be subjected to great distortion during the flight of 

 the bird. 



There was the mesh- work characteristic of sarcosporidian cysts, 

 the meshes being coarser at the periphery and finer in the centre. 



In the former position they measured from 10-20 p. across; in the 

 latter they were as small as 1-2/*. 



In the material on which this study is based the cysts, being mature, 

 lie between the muscle fibres and not within them. 



Stiles, studying the parasites of five ducks, found intermuscular 

 cysts alone in four, but in the fifth specimen both intermuscular and 

 intramuscular stages were seen. He states that in the latter, the 

 cysts were thinner and showed no non-staining central core. Although 

 Stiles suggested that they were only developmental phases of the same 

 form, he followed Blanchard's classification, calling one Balbiania rileyi 

 and placing the other in the genus Sarcocystis. It is now known that 

 the distinction between inter- and intramuscular positions is only a 

 question of development. The young stages lie within the muscle 

 fibre, but as they grow they become too large to be contained within it. 

 According to Minchin, the originally parasitized fibre is ruptured and 

 the cyst escapes. It seems more probable, however, that the fibre is 

 merely almost wholly destroyed, its remnants remaining around the 

 parasite as an adventitious cyst. However this may be, in the present 

 case, the parasites were inclosed within a tightly stretched membrane, 

 showing a considerable number of long, narrow nuclei. This was 

 derived from the host. The actual cyst membrane is very thin, 

 homogeneous, and part and parcel of the net work. 



The compartments, as we have seen, grow progressively smaller 

 from without inwards. Within them are the spores. 



These, in the peripheral compartments, are seen to be elongated 

 elements radially arranged. That is, as seen in the cross section of 

 the cyst, the spores are in more or less definite files directed along the 

 radii of this cross section. 



In the central portion of the central core, the meshes of the net are 

 filled with debris, which stains only with the plasma stain. Further 

 out, however, it is frequently possible to see that this debris is more 

 or less well divided up into little aggregates, doubtless each such 

 aggregate standing for a spore which has died and disintegrated. 

 In such situations chromatin masses are also frequent, following the 



