THE MYXOSrORIDIA, OR PSOROSPERMS OF FISHES. 81 



of granules originate. Daring the subsequent progress in development 

 up to tlie ripe psorospenn, changes take place in the form of the vesi- 

 cles, the character of the contour, and the contained corpuscles. The 

 latter first elongate, one pole becomes sharpened, the whole corpuscle 

 assumes the familiar clearness of outline, the granules diminish in 

 number and form (perhaps through fusion or after previous solution) 

 the 4 capsules. The contour of the sporoblast also becomes sharp. 



Lieberkiihn (see GMoromyxum mucronatum, p. 265) first noted tliei^an- 

 sporoblast as a solid plasma-sphere, but he did not trace the connection 

 of the solid sphere with Leydig's vesicles. 



In 1880, Gabriel noted, in MyxMium, lieherJcilknii (see p. 287), that the 

 vacuole stage of the pansporoblast is a subsequent and not the original 

 condition. It is quite evident, however, that he did not understand 

 the mode of pansporoblast formation. 



In 1881, Biitschli^ showed that the pansporoblast is primarily not a 

 vacuole, but a plasma-sphere. The segmentation of this and the devel- 

 opment of the resulting sporoblasts were also traced. 



Formation and segmentation of the pansporohlast. — The first step in 

 pansporoblast formation is the condensation around each of the numer- 

 ous nuclei (of the endoplasm) of a small clear-contoured sphere of myxo- 

 plasm, which seems limited by a thin envelope resulting from a conden- 

 sation of its peripheral layer, the whole constituting a pansporoblast. 

 This subsequently shrinks slightly, so as to appear as a ball surrounded 

 by a vacant space, and this latter in its turn by the membrane. The 

 nucleus then divides (by karyokinesis) and redivides so that one very 

 soon has a sphere (pansporoblast) with a dozen nuclei. The sphere 

 then segments into two hemispheres (sporoblasts) which remain sur- 

 rounded by the original pansporoblast membrane. Each sporoblast 

 contains several nuclei (see belowj. The nuclei which do not enter into 

 the formation of the two sporoblasts are rejected and are found in a 

 small mass of protoplasm which remains (along with the two sporo- 

 blasts) within the original pansi)()roblast membrane. 



In this connection it is well to quote from Kunstler and Pitres^ the 

 following erroneous description: 



This envelope [the ectoj)lasm] would contain, according to Biitschli, small nuclei. 

 The nuclei, in proportion as the cyst [membraned myxosporidium] enlarges, divide; 

 the protoplasm is condensed around them to form oval bodies, which Balbiant considers the 

 spores; this author has indeed seen there the formation of four falciform corpuscles [italits 

 my own, for errors]. 



'Ztschr. f. wiss. Zool., xxxv, pp. 645-640; Bronn's Tliier-Reich, 1882, i, p. 596. 

 -Description based upon Thriohau's (Compt. Rend. Acad. Sci. Paris, 1890, cxi, 

 p. 693). P'or the process in the Cruptocystes, see p. 201, 

 3 Jonrn. de Microgr., 1881, viii, p. ill. 

 F C 92 



