74 REPORT OF THE COMMISSIONER OF FISH AND FISHERIES. 



enters ujion an intracellular existence, penetrating into the interior 

 of the red blood and other cells of the host, where, protected b y the 

 cell membrane, it grows Ijy 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 amoeboidly, 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 following structure: 



In outline it is vermiform, sacculated, roundish or not infrequently 

 entirely irregular (see pis. 29, 37-39, 43-45). It usually possesses the 

 power of amoeboid movement and generally exhibits a distinct separa- 

 tion of ectoplasm and endoplasm (see pi. 39, figs. 1, 2, and pi. 44, fig. 1). 



The ectoplasm (see pi. 16, fig. 4; i>l- 3^? ^8- Ij ^I'd P^- 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 i)l. 44, fig. la). 



The endoplasm (see pi. 37, fig. 4; pi. 38, fig. 1, and pi. 39, fig. 1) 

 is more or less coarsely granular and contains numerous nuclei, fat- 

 globules, h;ematoidin crystals (pi. 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 hoematoidin 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 form a pale, solid globule termed the pansporo- 

 blast (pi. 12, fig. 1 a^c, and pi. 47, fig. 1 a, h) which later segments into a 

 number of sporoblasts (pi. 12, fig. 1 h, i, and pi. 47, fig. 1 c, d), each of 

 which develops into a spore. 



2. Spore. — This always contains three elements, shell, capsule with 

 filament, and siioroplasm. The shell (see pi. 16, fig. 3, and pi. 28, fig. 1) 

 is exceedingly transparent, very resistant to chemical reagents, and is 

 frequently bivalve. The capsule (pi. 26, fig. 7, cap.) is a pyriform, 

 hollow, elastic-walled body which always contains a single coiled 

 thread {fiUmient) capable of extrusion. The sporoplasm (pi. 26, fig. 

 7, spo.) is always a single mass of protoplasm. It contains nuclei (w), 

 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 (pi. 15, fig. 7 i), which, now 

 become the myxosporidium, rebegius the life cycle. 



