THE MYXOSPORIDIA, OR PSOROSPERMS OF FISHES. 179 
Plasmode encystment thus differs from that of simple amabz only in the fact 
- that the conditions observed in the ameba cyst (granular state of the protoplasm, 
vanishing 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 motile stage. 
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 (pl. 4, fig. 5 N), around which, 
later, portions of protoplasm segregate themselves from the remainder. In this way 
the spores are formed. Thus in a simple ameeba cyst, 10 hours after the falling to 
pieces of the nucleus, 6 spores (pl. 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 spores 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 (pl. 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 
(pl. 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 (pl. 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 10j (simple amceba 
cysts) to 30 to 604 (plasmode cysts); often also elongate-oval spore tubes are found 
70 long and 24 broad. . 
Spores: Length, 3:3 to 4u, oval or pyriform (pl. 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 hody a globular, very strongly 
refringent, homogeneous nucleus (N), 1:64, is found. The spores thus originating 
still further increase through a somewhat oblique-running, transverse division, the 
nucleus dividing karyokinetically (pl. 5, fig. 10a-1). Division was followed intra 
vitam, and the study completed in specimens fixed with chromo-aceto-osmie acid 
and stained with hematoxylin. 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 (pl. 5, fig. 10h) 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 homogencous character, acquiring a netted, 
honeycomb-like structure (pl. 5, fig 10a) with tolerably strongly staining granules. 
This netted form passes into an elongate, striate-fibered structure (b), 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 strix, in which 
the chromatin granules are imbedded. These latter become concentrated toward 
the equator, when a so-called nuclear plate (c) forms, which consists of baculiform 
