THE MYXOSPORIDIA, OR PSOROSPEKMS OF FISHES. 179 



Plasmode encystment thus differs from that of simple amcebaj only in the fact 

 that the conditions observed in the amoeba cyst (granular state of the protoplasm, 

 vnnishiug of the nucleus, or, in other words, its peculiar falling to pieces into indi- 

 vidual small nuclei) wear themselves off with the jilasmodes during their motile stage. 



3. Spore formation. — Beginning about 3 days after encystment; not originating 

 through successive division of the nucleus aud protoplasm, the nucleus falling to 

 pieces into several small, strougly refringent corpuscles (pi. 4, fig. 5N), around which, 

 later, portions of protoplasm segregate themselves from the remainder. In this way 

 the spores are formed. Thus in a simple amojba cj-st, 10 hours after the falling to 

 pieces of the nucleus, 6 spores (pi. 4, fig. 6) were seen, eacli with a small globular 

 nixcleus. Besides these, the cyst still contained plasma in which were seen, along 

 with many small, strongly refringent granules, isolated small, round nucleiform 

 structures (N). About 24 hours later the number of spores had doubled; neverthe- 

 less, there was still jjresent undifferentiated i)lasraa as well as nuclei. After 24 hours 

 more the number of spores had so increased as to entirely fill the cyst; no free 

 protoplasm remained (pi. 4, fig, 7). 



Spore formation in the plasmode cysts (also accurately followed) takes place in 

 the same way. In plasmode cysts containing numerous small nuclei (very probably 

 originating through successive divisions of the nucleus) are formed small bodies, 

 globular to oval, delimited from the surrounding protoplasm by a delicate membrane 

 (pi. 5, fig. 4), fine-grained, some allowing a small, globular nucleus to 

 [Page 22] show through. After about 6 hours these bodies acquire a somewhat pyri- 

 form shape, the membrane becomes thicker and sharper, the protoplasm 

 more hyaline, the nucleus thus becoming more distiuctly visible. This transformation 

 proceeds so that after 24 to 36 hours the bodies are pyrifnrm, sharply contoured, com- 

 pletely hyaline spores (pi. 5, fig. 5), in which a globular nucleus is always plainly 

 visible. Along with this transformation new spores are formed from the surrounding 

 protoplasm, until all the free protojilasm is used up, the cysts transforming them- 

 selves into spore cysts or spore tubes. Number of spores in cyst variable, dependent 

 upon the size of the cyst, whose diameter varies from about 10// (simple amoeba 

 cysts) to 30 to 60/t (plasmode cysts) ; often also elongate-oval spore tubes are found 

 lOjLi long and 24// broad. 



Spores: Length, 3*3 to 4//, oval or pyriform (pi. 5, fig. 8), rather strongly refrin- 

 gent, completely hyaline, bounded exteriorly by an extremely thin homogeneous 

 layer, the pellicula. In the broader end of the body a globular, very strongly 

 refringent, homogeneous nucleus (N), 1"6//, is found. Tlie spores thus originating 

 still further increase through a somewhat oblique-running, transverse division, the 

 nucleus dividing karyokinetically (pi. 5, tig. 10a-?). Division was followed intra 

 ritavi, and the study completed in specimens fixed with chromo-aceto-osmic acid 

 and stained with hajmatoxyliii. Nuclear division, requires about ^ hour, and pro- 

 ceeds in about the same way as that of the micronucleus of the ciliated Infusoria. 

 The membrane or external border-layer of the nucleus remains quiescent during the 

 whole process, only in the last stages (pi. 5, fig. 10/() appearing some- 

 [Page 23] what indistinct preliminary to reappearing with distinctness in the 

 daughter nuclei. 



Owing to the small size of the nucleus, karyokinesis could be followed only in the 

 principal steps. The first alteration observed in the nucleus is a marked increase 

 in size; simultaneously it loses its homogeneous character, acquiring a netted, 

 honeycomb-like structure ( pi. 5, fig 10a ) with tolerably strongly staining granules. 

 This netted form passes into an elongate, striate-fibered structure (6), the nucleus at 

 the same time enlarging and assuming an ellipsoid form whose long axis coincides 

 with that of the spore. Between the nuclear poles run meridional strife, in which 

 the chromatin granules are imbedded. These latter become concentrated toward 

 t}je ecjuator, wljen a so-called nuclear plate (c) forms, which consists of bacuUforn^ 



