THE MYXOSPORIDIA, OR PSOROSPERMS OF FISHES. 81 



of grannies originate. Dnring tlie snbseqneut progress in development 

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

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

 latter first elongate, one ])ole 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 contonr of the sporoblast also becomes sharp. 



Lieberkiihn (see Ghloromyxum mucrofiatiim, p. 265) first noted the pan- 

 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 My.rldium lieherlcilhnU (see p. 287), that the 

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

 condition. It is (luite 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. 



PROCESS.* 



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

 pansporoblast formation is the condensation around eachof the numer- 

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

 plasra, which seems limited by a tliin envelope resulting from a conden- 

 sation of its x>eripheral 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 inembrane. 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 below). 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 pansporoblast membrane. 



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

 following erroneous description : 



This euvelope [the ectoplasm] -woukl contain, according to Biitschli, small nuclei. 

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

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

 spores; tJds author has indeed seen there the formation of four falciform corjjuscles [italics 

 my own, for errors]. 



iZtschr. f. wiss. ZooL, xxxv, pp. 645-646; Bronn's Thier-Reich, 1882, 1, p. 596. 

 2 Description base^ upon Thelohan's (Compt. Rend. Acad. Sci. Paris, 1890, cxi, 

 p. 693). For the process iu the Cri/piocystes, see p. 201. 

 '^ Journ. de Microgr., 1884; viii, p. 471. 



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