A NEW MYXOSPORIDIAN PARASITE. 3 



It is a remarkable fact that the trophozoites never extend to the 

 sarcolemma, there being always a thin layer of sarcoplasm and muscle 

 fibrils between the two. This is well shown in Figures 4 to 6, where 

 the peripheral laj^er of fibrils and sarcoplasm can be distinctly seen. 

 As shown in the figures the trophozoites vary considerably in size, 

 some being several times the length of others. The length of those 

 measured varied from 2 to 6 mm. The size of the mature tropho- 

 zoite appears to be dependent on the number present hi a fiber, since 

 the diameter of the fibers containing fully dev- eloped trophozoites 

 is remarkably uniform. There may be as many as six trophozoites, 

 or possibly even more, in a fiber. In all cases observed by the writer 

 they were arranged in a single row extending from one end of the 

 fiber to the other, but in Thompson's figures several trophozoites 

 are shown lying side by side. 



Fig. 6. — Cross section of an infected fiber showing the tropliozoite filled with spores and 



surrounded on all s^ides by a portion of the muscle fiber. X 190. 

 Figs. 7 and 8. — Spores viewed from the side. X 2,500. 

 Figs. 9 and 10. — Polar views of spores. X 2,500. 



Only sporulating trophozoites were found in the fish examined 

 by the writer, the spores forming the whitish, granular mass previ- 

 ously referred to. Surrounding the spores is a thin but distinct 

 layer of ectoplasm (figs. 4 and 5). Just within the ectoplasm can 

 be seen numerous free nuclei and pansporoblasts in different stages 

 of development. Evidently, as in many other myxosporidia that 

 form cysts in the tissues, the development of the spores takes place 

 in a comparatively narrow zone just within the ectoplasm. 



The spores (figs. 7 to 10) are subspherical, asymmetrical, and con- 

 tain but one capsule. The shell is thin and the sutural line in- 

 distinct. There is usually a slight indentation along the sutural 

 line on the postcapsular side. The shell valves are very unequal in 

 size, that containing the capsule being much larger than the other, 

 which is evidently degenerate. The capsule is relatively large and 

 appears spherical in shape except when viewed from the side, when 

 a short neck can be distinguished connecting it with the shell (figs. 7 

 and 8). 



