THE MYXOSPORIDIA, OR PSOROSPERMS OF FISHES. 217 
Cyst.'.—Exelusively confined to the branchial lamelle, appearing by 
reflected light as white pustules, usually elongate-oval, 2 to 3mm. long; 
with greater development distending the flat branchial lamella. On 
closer examination of the freshest possible branchiz, the cysts are seen 
to be neither extra-, nor intra-, but sub-epithelial, the blood vessels 
of the mucosa running over their surfaces. Their seat is thus the 
submucous connective tissue layer which immediately surrounds the 
supporting central cartilaginous rod of the lamella, and which underlies 
each and separates both of the layers of inucous membrane, which 
latter form the opposite faces of the lamella and in which run, super- 
ficially, the afferent and efferent blood vessels and the capillaries of the 
mucosa. One can easily convince himself of this situation of the 
myxosporidium by external observation. One then remarks that the 
transverse-running capillaries superficially girdle the myxosporidium. 
A transverse section through the mass thus shows the supporting cen- 
tral cartilaginous rod girdled by the myxosporidium, and the latter in 
its turn surrounded by the vascular layer of the mucosa. If the myx- 
osporidium attain a greater growth, it naturally distends the lamellee — 
more and more, and, since the transverse capillaries girdle the myxo- 
sporidium ring-wise and oppose an obstacle to its expansion, the latter 
structure bulges out, sac-like, in the intervals between them, its whole 
outline being thus multilobate. From some further observations on 
very large myxosporidia, Biitschli believes that finally, through the 
continued growth of the myxosporidium, the restraining capillaries 
become ruptured, which explains the blood extravasations observed by 
him in the superficial portions of large myxosporidia, the girdling 
capillaries in these cases being absent. 
Membrane: By eareful manipulation the myxosporidium can some- 
times be removed intact from its seat in the branchiz. In both of the 
two successful instances, Biitschli observed a distinct membrane which 
possessed special interest in differing from the type usual among the 
unicellular organisms and particularly from that found in the Gregarines. 
Itis of a plasmatic nature, being composed of clear, very finely granular 
protoplasm, in which numerous small nuclei are imbedded. Neither 
acetic acid nor staining reactions show any evidence of cell outlines. 
The finely granular nuclei possess a distinct dark membrane, show a 
somewhat irregular outline, and stain intensely with alum carmine. It 
is difficult to determine with certainty whether this membrane is a 
production of the myxosporidium or of the tissues of the host. As 
opposing the former view (a view which, however, Biitschli considers as 
in no wise excluded) is the fact that the nuclei of the membrane are 
somewhat larger than those found in the endoplasm. 
1The description is Biitschli’s. He calls it the myxosporidium, but it appears 
from his description to be the cyst (which, however, is probably only a later stage 
of growth of the imbedded myxosporidium). Pfeiffer erroneously states that these 
observations were madeupon Perca fluviatilis (Die Protozoen als Krankheitserreger, 
2 ed., 1891, p. 130). 
