THE MYXOSPORIDIA, OR PSOROSPERMS OF FISHES. 223 



Spore formation.— ^YiiAx the growth the number of nuclei increases by successive 

 divisions ' (ni;iny of which were seen to occur). Subsequently eacli nucleus con- 

 donk^es around it some of the myxoplasm, thus forming the pansporoblasts. These 

 "■row, become elliptic, and the rudiments of the capsules appear in them, at first as 

 very pale, then as brilliant bodies. The mode of their development was not entirely 

 satisfactorily ascertained. They usually develop 2 in each pansporoblast, some of 

 these sporoblasts containing 3 granular globules, 2 small and 1 large, which prob- 

 ably develop respectively into the capsules and the sporoplasm. Also incompletely 

 developed spores were seen inclosing elements believed to be capsules in process of 

 development. These were: (1) Two spherical vesicles containing each a small cen- 

 tral globule placed in the substance of the spore remote from the poles. (2) Two 

 small similar vesicles placed one beside the other at one pole. (3) Two pyriform 

 vesicles with a small central globule, sometimes remote from each,other, sometimes 

 approxinuited to each other and situated at one extremity of the spore. These vesi- 

 cles were no doubt the small organs with spiral filaments. Their origin could 

 not be cleaiiv determined. 



^^ore.— Flattened-ellipsoid, rather elongate, the two ends similar; 

 length 12 to 15 ir, breadth 9 to 11 /q length of capsules 4 //; nuclei of 

 capsulogenous membrane persisting to maturity of spore; vacuole 

 present; nuclei originating by continued division from a primitive one, 

 not more than 4; when of this number, 2 are situated before and 2 

 behind the vacuole (Thdlohan, pp. 209-210). 



Degenerate forms [of this species i] from the gall bladder may have 

 3 capsules or none, and the bivalve character of the shell maybe absent 

 (Pfeifier). 



Eibbons : Balbiani ^ has made some curious but dubious observations, 

 arriving at conclusions which by no means accord with the general 

 consensus of opinion. He describes an elastic, ribbon-like process 

 (the rihhon) as existing along the border of each valve of the shell, 

 stating that at the time of maturity of the spore (the only period at 

 which such ribbons are visible, as at other periods they are closely 

 appressed to the valves) they become unrolled and recurved, such action 

 resulting in the splitting apart of the valves and the consequent release 

 of the amceboid sporoplasm. The ribbons divide at their distal 

 extremity into 2 or 3 ribbonettes. These elastic structures he regards 

 as comparable to the cruciform elastic filaments (elaters) of the Equise- 

 tum spore, remarking that in the Myxosporidia they serve a different 

 function, their action here being valve-separation and not spore-disper- 

 sal. He further says that these elastic ribbons have another function, 

 viz, to maintain contact of 2 spores during what he regards as a state of 



I From Balbiani's language it is plain that he did not recognize the vacuolic 

 nature of Biitschli's "nucleus." Still he must have seen nuclei (and not vacuoles) 

 in the later myxosporidiura stages, as he states that he repeatedly observed them to 

 divide. Probably Thflohan's observation of karyokinetic division (Compt. Rend. 

 Acad. Sci. Paris, 1890, cxi, p. 693) was upon M. elUpsoides, though itisnot distinctly 

 BO stated. Among other figures he saw a spindle with an absolutely typical equa- 

 torial plate. 



^ Jouru.de Microgr., 1883, vii, pp. 276-7: L65ons sur Ics Sporozoaires, 1884, pp. 

 142^. 



