74 REPORT OF THE COMMISSIONER OF FISH AND FISHERIES. 
enters upon an intracellular existence, penetrating into the interior 
of the red blood and other cells of the host, where, protected by the 
-cell membrane, it grows hy feeding on the cell contents. Finally, 
its continued growth produces distension, and ultimately rupture of 
the cell-membrane, and the myxosporidium becomes free. It now 
moves about ameeboidly, grows larger, the nuclei become more num- 
erous through karyokinesis, and spore formation begins. This last 
process is not confined to the last stages of the life cycle, but begins 
early and is progressive. 
At this period the myxosporidium exhibits the followin structure: 
In outline it is vermiform, sacculated, roundish or not infrequently 
entirely irregular (see pls. 29, 37-39, 43-45). It usually possesses the 
power of ameboid movement and generally exhibits a distinct separa- 
tion of ectoplasm and endoplasm (see pl. 39, figs. 1, 2, and pl. 44, fig. 1). 
The ectoplasm (see pl. 16, fig. 4; pl. 39, fig. 1; and pl. 44, fig. 3) is 
very transparent, quite or nearly destitute of granules, sometimes more 
or less radiate-striate, and is often prolonged into pseudopodia which 
only involve the endoplasm when of very large size. The pseudopodia 
sometimes form a shaggy or bristly coat over the whole, or a part of 
the myxosporidium (see pl. 44, fig. 1a). 
The endoplasm (see pl. 37, fig. 4; pl. 38, fig. 1, and pl. 39, fig. 1) 
is more or less coarsely granular and contains numerous nuclei, fat- 
globules, hematoidin erystals (pl. 44, fig. 5) and other pigment. The 
nuclei are derived from the primitive nuclei of the myxosporidium (the 
nuclei of the sporoplasm; see below). The hiematoidin crystals are 
usually found within the fat-globules. The myxosporidium may contain 
other extraneous pigment, e. g., bile-, and perhaps a proper, pigment 
(see pp. 76, 277). 
Spore formation: Each nucleus attracts to it a portion of the sur- 
rounding myxoplasm to forma pale, solid globule termed the pansporo- 
blast (pl. 12, fig. 1 a-c, and pl. 47, fig. 1 a, b) which later segments into a 
number of sporoblasts (pl. 12, fig. 1 h, 7, and pl. 47, fig. 1 ¢, d), each of 
which develops into a spore. 
2. Spore.—This always contains three elements, shell, capsule with 
filament, and sporoplasm. The shell (see pl. 16, fig. 3, and pl. 28, fig. 1) 
is exceedingly transparent, very resistant to chemical reagents, and is 
frequently bivalve. The capsule (pl. 26, fig. 7, cap.) is a pyriform, 
hollow, elastic-walled body which always contains a single coiled 
thread (filament) capable of extrusion. The sporoplasm (pl. 26, fig. 
7, spo.) is always a single mass of protoplasm. It contains nuclei (7), 
and sometimes a vacuole (fig. 7, vac.), which when present is always 
single. At maturity the shell splits when bivalve, or dissolves when 
univalve, thus setting free the sporoplasm (pl. 15, fig. 7 6), which, now 
become the myxosporidium, rebegins the life cycle. 
