THE MYXOSI'ORIDIA, OH PSORORPERMS OF FISHES. 



201 



never showed, iinder tlic most carefal microscopic examination, the 

 slightest trace of infection (Ilennegiiy and Thelolian, 1892). 



Season. — Disease most frequent and at maximum of development 

 from about July 15 to the end of August; number affected diminishing 

 in September; diminution more pronounced in October; disappearing 

 entirely after November 15; reappearing about March 15 or the first 

 da5\s of April. 

 32. Thelohania giardi Heiiiieguy, 1892. PI. 12, figs. 1, 2. 



* Cranguon ; error. 



Cyst unknown. 



Sjjore formation. — Pansporoblast sidierical; diameter 14 // (12 to 

 11 yu); in the young stages consisting of a very thin membrane 

 resisting potassium hydrate, inclosing a very transparent, scarcely 

 granular, slightly refringeut protoplasm, having at its center a rather 

 large nucleus (pi. 12, fig. la, h), often visible in the fresh state, becoming 

 much clearer under the action of reagents. 



(1) Segmentation of the pansporoblast: The nucleus first presents 

 the typical resting structure with a distinct membrane. The chromatin 

 can take on different arrangements, sometimes formingone grain much 

 larger than the others, sometimes a variable number of smaller sub- 

 equal grains, or sometimes crowded back against the membrane, pre- 

 senting here and there thicker portions (pi. 12, fig. 1). Subsequently 

 a remarkable modification occurs: the chromatin has become arranged 

 in filaments, the membrane has disappeared, and the nucleus assumes 

 the arrangement known as the chromatic coil; very soon the chro- 

 matic filaments orient themselves into a very distinct equatorial plate, 

 which becomes double, the process resulting in the formation of 2 

 daughter-nuclei. We thus have a true karyodieresis. The achromatic 

 filaments were not seen, doubtless owing to their rather small size and 

 partly, Ilenneguy and Th^lohan believe, to the nature and optical proper- 

 ties of tlu^ i)rotoplasm. Protojilasmic segmentation soon follows nuclear 

 division, and one sees, within the primitive pansporoblast membrane, 2 

 small distin^'t nucleated masses. In their turn these 2 masses divide 

 and redivide, the process ending with the formation of 8 small ])lasmic 

 bodies [sjyorohlasts) within tiic original pansporoblast membrane. The 

 divisions do not take place very rai)idly, and between successive ones 



