THE MYXOSPOKIDIA, OR PSOROSPKRMS OF FISHES. 219 



often almost circuliir, antorioi- end only slightly atteuuated, border of 

 suture exliibitiug folds or criini)ings varyiiis: in number from 7 to 0. 



Shell: Substance dark and somewhat glittering, i)ossessing a marked 

 resistance to chemical reagents; warmed with concentrated sulphuric 

 acid the valves fjill apart; stronger heating ett'ects their comjdete 

 destruction. Valves 2, superior and inferior, with a tolerably thick 

 ridge or welt along the border (line of junction), visible very plainly as 

 a ridge on transverse view. 



Capsule : Wall tolerably thick, glittering, inclosing a cavity occupied 

 by the coiled filament which appears paler thun the wall; showing, 

 with the normal extrusion of the lilaments, a very noticeable diminu- 

 tion of volume, whence the conclusion that (as with the thread-cells 

 proper) such extrusion is the result of tlie pressure of the stretched 

 elastic capsular walls. The capsules are destroyed by gently warming 

 with concentrated sulphuric acid. Filaments extruded under the 

 intiueuce of potassium hydrate solution, glycerin, and especially con- 

 centrated sulphuric acid; also by mechanical pressure. The extrusion 

 produced by the last means is frequently abnormal and very irregular, 

 the filament being ejected in a more or less spiral form, or only incom- 

 pletely, or sometimes through a rupture in the capsular wall, either into 

 the shell cavity, or through the shell, or, in the last case, more probably 

 between the (by the pressure) partially loosened valves. Biltschli addsa 

 few interesting remarks to the effect that the capsules, so constant in 

 the Myxosporidia, doubtless have some important and yet to be discov- 

 ered function. 



Sporoplasm: Mostly very delicate, cloudy, granulated, nearly filling 

 the posterior portion of the shell cavity, projecting forward in the 

 median line and on the outer side of the capsules; this projection could 

 not be traced all the way around the capsules. Containing a variable 

 number of granules. Vacuole,' frequently quite plainly visible even 

 in the fresh state as a circular or oval clear spot. It becomes more 

 prominent, however, after the addition of dilute acetic acid or iodine 

 solution and then shows a dark, somewhat granulated membrane and a 

 number of rather i)ale granules strewn through the contents, resisting 

 all stains,^ according to Biitschli sometimes invisible, a result that he 

 attributes to great condensation of the protoplasm. Some spores 

 appeared to possess 2 vacuoles, but upon this point Biitschli was not 

 certain. 



'This is Biitschll's description of liis "imclou.s." 



-A circumstance explained (but erroneously) by Biitschli as being due to a failure 

 of the stain to permeate the sliell. He says the noustaiuinf;; can not be taken as a 

 contraindication of the nuclear nature of the structure in ([uestion, as the protoplasm 

 also resists the stain. From my own experience I should say that would dejieud on 

 the kind of stain, used, i>lasmatic stains ireuerally being, nuclear stains generally not 

 being, retained. 



