THE MYXOSPORIDIA, OR PSOROSPERMS OF FISHES. 251 



aeuate posterior extremity, destitute of apparent structure,' very 

 liable to break off, the fracture always taking' place evenly and never 

 producing a ragged end. Lateral pieces 2, strongly curved, extend- 

 ing forward on either side from the anterior end of tlie median piece, 

 applied closely to the rounded posterior portion of the shell about as 

 far forward as the junction of the posterior and nuddle thirds of its 

 outer margin; thickest at their origin, becoming very thin toward their 

 anterior extremities. They have a slight expansion over the superior 

 and inferior surfaces of the shell, thus tending to form a slightly cup- 

 shaped receptacle for it. It is probable that they really extend forward 

 along upon the surface and over the sides of the ridges, which struct- 

 ures appear as though continuous with them. 



Capsules: 2, pyriforra, somewhat diverging posteriorly, attenuated 

 at the anterior end into the ducts which converge forward toward the 

 median line, on either side of which they open. Capsular wall staining 

 readily with and retaining tenaciously bismarck brown and fiichsin; 

 rendered transparent by iodine water and by strong ammonia water. 

 The filaments are thus seen lying coiled within the capsule. They 

 appear not to stain with reagents which stain the walls, the capsule 

 usually showing a lighter central and a darker circumferential portion. 

 Eelative to the occasional presence on or near the capsule of a dark 

 "granule," see p. 220. The capsules are always surrounded by a 

 clear space, the i)ericystic. This space never shows a double contour, 

 never stains, and presents no appearance suggestive of an outer mem- 

 brane. It is apparently a natural and presumably (by exclusion and 

 analogy) a fluid-filled space. It does not stain with iodine, agreeing 

 in this respect with the space (with which it is continuous) everywhere 

 lining the inner surface of the shell, and differing in the same respect 

 from the vacuolic space. 



Sporoplasm: Inferior surface convex in all directions, showing a 

 rounded posterolateral margin,^ extending from abont the middle point 

 of the lateral border of the spore on one side to the corres])onding point 

 on the opposite side. From these two points (infero-lateral cornua) 

 the 2 anterolateral borders curve inward and forward with a sharji 

 anteriorly directed concavity to tlie median line where the sporoplasm 

 is drawn out to a point (the infero-median cornu) which forms also the 

 inferior extremity of a ridge shortly to be described as the supero- 

 inferior intercornual ridge. The infero-median cornu is situated about 

 at the level of the middle point of the antero-posterior diameter of the 

 shell cavity. Lateral surface, extending forward for some distance 



• Iodine (aqueous sohition with potassium iodide) produces a decided beadin<j of 

 the median piece, transverso lines of division appoaiinf]^, constituting a <lc(ided 

 pseudo-seginentajtion. My attention was directed to this ithenonionon by Dr. Stiles. 



* Common, of course, to it and to the superior surface, being the line, of intersec- 

 tion of the longitudinal plane with the interior surface of the shell. 



