2 U. S. BUREAU OF FISHEEIES. 



nun., while that of the uninfected fibers was about 0.2 to 0.4 mm. 

 These measurements are somewhat Greater than those given by 

 Thompson. Possibly the discrepancy "may be due to a difference in 

 the size of the fish, that examined by the writer having a total 

 length of about 5 feet. 



Figs. 1, 2. and 3. — Portion of muscle fibers showing the arrangement of the parasites 

 within tlie fibers. X 20. 



Fig. 4. — Cross section of a small portion of an infected muscle fiber. The cut ends of the 

 fibrils are shaded black. Within the fibrillar layer can be seen a portion of the tropho- 

 zoite surrounded by a distinct ectoplasmie layer. X 57.'j. 



Fig. 5. — (,'ross section of a portion of an infected fiber showing the overlapping ends of 

 two trophozoites. This is a somewhat later stage than Figure 4, and the fibrils are 

 beginning to degenerate. X575. 



When examined under the microscope, the infected fibers were 

 seen to contain a number of elongated trophozoites arranged ih a 

 single row within the fiber but usually overlapping more or less at 

 the ends (figs. 1 to 3) . In every case the parasites extended practically 

 the entire length of the fiber. This condition was also noticed by 

 Thompson, who suspected they were trophozoites of a sporozoan but 

 was unable to definitelv determine their nature. 



