THE MYXOSPORIDIA, OR PSOROSPERMS OF FISHES. 217 



CysV — Exclusively confined to the branchial lamelhTc, appearing by 

 reflctited light as white pUvStules, usually elongate-oval, 2 to 3 nun. long; 

 with greater development distending the flat branchial lamellae. On 

 closer examination of the freshest possible branchiae, 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 mucous membrane, which 

 latter form the opposite faces of the lamella and in Avhich 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 laj^er of the mucosa. If the myx- 

 osporidium attain a greater growth, it naturally distends the lamelhp, 

 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 careful manipulation the myxosporidium can some- 

 times be removed intact from its seat in the branchitie. 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. 

 It is of a plasmatic nature, being composed of clear, very finely granular 

 protoplasm, in which numerous small nuclei are imbedded. ISTeither 

 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 dififlcult 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. 



'The 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 made upon Pcrca Jiuviatilis (Die Protozoen als Kraukheitserreger, 

 2ed., 1891, p. 130). 



