THE MYXOSPORIDIA, OR PSOROSPERMS OF FISHES. 193 



1 Cyst structure} — Number, 1 to i (sometimes a dozen, Tlieloliaii), rarely 

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

 as a small pea, some, liowever, attaining only tlie 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 whicli 

 yield bubbles of gas (COj?) with mineral acids. I\riiller (1811, p. 491) 

 found also some microscopic crystals. Thelohan (1890, p. 20i) adds that 

 the average thickness is 5 //; under high powers the membrane sliows 

 a fibrillary structure parallel to the surface of the cyst. Tlielohan 

 believes the membrane to be uonnucleated and considers this a strong 

 argument in favor of its derivation from the similarly uonnucleated 

 myxosporidiau ectoplasm. 



MijxosporkUum. — Spore formation r^ 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, 3 to 5 /< long, 



2 to 3 II broad, size and form constant in spores from the larger cysts, 

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

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

 Interior of sj)ore showing a shaded portion at the smaller, and a clear 

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

 (50 /<), 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. Thelohan (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 (C02'?), 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, Thelohan found to be gen- 

 tian violet; but above all, safVanin by the Gram-Bizzozero method. 



Habitat. — Subcutaneous cysts of Gastcronteus aculeafus (sticklel)ack) 

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

 (Miiller). Subcutaneous cysts of Fygosteus pungitius (9-spiued stickle- 



' Description Gltigo's unless otherwise stated. 



'^Tlidloliau's ob.sc'rvations on a niyxospoiidiuin in G. aciilcatits (Journ.do ^licrogr., 

 1891, XV, p. 147). 



F C 13 



