/ 
THE MYXOSPORIDIA, OR PSOROSPERMS OF FISHES. 193 
i Cyst structure..—Number, 1 to 4 (sometimes a dozen, Thélohan), 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 pin’s head; 
size of tumor bearing no relation to that of the fish, being variable in 
the same individual; shape regularly spherical or only a little rounded; 
color usually whitish—when covered by the epidermis of the fish, 
_ silvery. Membrane always present, resistant, usually covered by the 
epidermis, which forms an outer cyst; surface granulated by alcohol; 
Contents consisting of a small quantity of a colorless fluid coagulable 
by alcohol, holding in suspension immense numbers of corpuscles which 
yield bubbles of gas (CO,?) with mineral acids. Miiller (1841, p. 491) 
found also some microscopic crystals. Thélohan (1890, p. 204) adds that 
the average thickness is 5 4; under high powers the membrane shows 
a fibrillary structure parallel to the surface of the cyst. Thélohan 
believes the membrane to be nonnucleated and considers this a strong 
argument in favor of its derivation from the similarly nonnucleated 
myxosporidian ectoplasin. 
| Myxosporidium.—Spore formation:? Myxoplasm containing 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. 
Spore.—Very numerous, transparent, regularly ovoid, 5 to 5 y-long, 
2 to 3 uw broad, size and form constant in spores from 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 long 
(50 4), extruded under the influence of iodine. No other reagent pro- 
duced such extrusion. The central (iodinophile) vacuole appears to 
be absent; a vacuole uncolorable by iodine is present, however, usually 
in the larger end, less frequently subcentral. Thélohan (1890, p. 212) 
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-chemistry.— Acetic acid produces no change. Sulphuric acid 
causes evolution 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 blood corpuscles 
(Gluge). The best stains for this species, Thélohan found to be gen- 
tian violet; but above all, safranin by the Gram-Bizzozero method. 
Habitat.—Subcutaneous cysts of Gasterosteus aculeatus (stickleback) 
in European rivers, occurring only once in every 20 or 30 fishes examined 
(Miiller). Subcutaneous cysts of Pygosteus pungitius (9-spined stickle- 
1 Description Gluge’s unless otherwise stated. 
2Thélohan’s observations on a myxosporidium in G. aculeatus (Journ. de Microgr., 
1891, xv, p. 147). 
F c——l3 
