THE MYXOSPORIDIA, OR PSOROSPERMS OF FISHES. 179 



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

 that the conditions observed in the amfeba cyst (granular state of the protoplasni, 

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

 vidual small nuclei) wear themselves off with the plasmodes during their motilestage. 



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

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

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

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

 the spores are formed. Thus in a simple araceba cyst, 10 hours after the falling to 

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

 nucleus. 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 sijores had doubled; neverthe- 

 less, there was still present undifferentiated plasma 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 distinctly visible. This transformation 

 proceeds so that after 24 to 36 hours the bodies are pyriform, 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 protoplasm 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// (plasmode cysts) ; often also elongate-oval spore tubes are found 

 70// 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 

 refringect, homogeneous nucleus (N), l"6/<, is found. The spores thus originating 

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

 nucleus dividing karyokinetically (pi. 5, tig. lOa-l). Division was followed intra 

 vitam, and the study completed in specimens fixed with chromo-accto-osmic acid 

 and stained with hrematoxylin. Xuclcar division, requires about i 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. lO/i) appearing some- 

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

 daughter nuclei. 



Owing to the small size of the nucleus, karyoklnesis could bo 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-fibored structure (b), the nucleus at 

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

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

 the chromatin {granules are imbedded. These latter become concentrated toward 

 the e(iuator, when a so-called nuclear plate (o) forms, which consists of baculiform 



