THE MYXOSPORIDIA, OR PSOROSPERMS OF FISHES. 193 



Cyst structure:-l^mnhev, 1 to 4 (sometimes a dozen, Thelohan), rarely 

 more, in contact or more or less widely separate; the majority as large 

 as a small pea, some, However, attaining only the size of a pms head; 

 size of tumor bearing no relation to that of the fish being variable in 

 the same individual; shape regnlarly spherical or only alitt.o ronnc^d; 

 color usually whitish-when covered by the epidermis of the fash 

 silvery. Membrane always present, resistant, usually covered by the 

 epidermis, which forms an outer cyst; surface granulated by alcoho ; 

 Contents consisting of a small quantity of a colorless fluid coagulable 

 by alcohol, holding in suspension immense ^^^nibers ot corpusc es which 

 vield bubbles of gas (CO.?) with mineral acids. Muller (18-41, p. 491) 

 found also sonie microscopic crystals. Thelohan (1890, p. 204) adds that 

 the average thickness is 5 ;.; under high powers the membrane shows 

 a fibrillary structure parallel to the surface of the cys Tlie lohan 

 believes the membrane to be nonnucleated and considers this a strong 

 argument in favor of its derivation from the similarly nonnucleated 



mvxosporidian ectoplasm. ' . . • n 



. MuJosporidinm.-^pove formation:^ Myxoplasm contamiDg small 

 nucleated globules which surround themselves with a thin membrane, 

 divide, and end by forming small spheres filled with very numerous 

 rounded nucleated elements which later will yield the spores. ^ 



^pore-Very numerous, transparent, regularly ovoid, o to o j.i long, 

 2 to 3 n broad, size and form constant in spores Irom the larger cysts, 

 less clear in those from the smaller. Shell bivalve; structure not 

 demonstrable; chemical characters the same as those of other spores. 

 Interior of spore showing a shaded portion at the smaller, and a clear 

 portion filling the larger, extremity. Capsule 1, filament very fong 

 (50 u) extruded under the infiuence of iodine. No other reagent pro- 

 duced such ^extrusion. The central (iodinophile) vacuole appears to 

 be absent; a vacuole uncolorable by fodine is P^^^^^^, however usually 

 in the larger end, less frequently subcentral. Thelohan (1890, p. .1.) 

 has traced the division of the nuclei up to 4, a number which he has 

 never seen (but which he does not wish to assert may not be) exceeded. 

 Micro-chemistnj.-Acetiii acid produces no change. Sulphuric acid 

 causes evolutfon of bubbles of gas (Co/?), the corpuscles at the same 

 time becoming less clear but not dissolving. Potassium hydrate causes 

 an agglomeration similar to the "rouleaux" of Wood corpuscles 

 (Gluoe). The best stains for this species, Thelohan found to be gen- 

 tian vfolet; but above all, safranin by the Gram-Bizzozero method. 



mZ>itot-Subcutaneous cysts of Gasterosteus aculeatus (stickleback 

 in European rivers, occurring only once in every 20 or 30 fishes examined 

 (Muller). Subcutaneous cysts of Fygosteus pungUius (9-spmed stickle- 



1 DescriDtion Gluffe's unless otherwise stated. 



.Shan's observations on a myxosporidiu.n in G. aculeatus (Journ. do M^crogr., 



1891, XV, p. 147). 

 FC 13 



