202 REPORT OF THE COMMISSIONER OF FISH AND FISHERIES. 



the nuclei liave time to return to a state of rest, whence they again pass 

 through the same stages preliminary to division. 



The sporoblasts have no regular arrangement within the pansporo- 

 blast membrane; their shape is inconstant, varying with their arrange- 

 ment; they generally ai)proximate a truncate-pyramidal form. Each 

 sporoblast develops into a spore. Spores thus contained 8 in each 

 pansporoblast membrane, without regular arrangement, not nearly 

 filling the cavity. This is the last stage of development reached in the 

 muscles of the host. 



Pansporoblast membrane retaining its original dimensions, perfectly 

 transparent, very thin, although the double contour is easily visible, 

 showing in optical section marked thickenings, often 2 in number (pi. 12, 

 fig. lA;). 



(2) Development of sporoblast into spore: Owing to the very minute 

 size of these bodies, it is almost impossible to follow this development 

 in detail or to con firm the facts discovered in the larger forms by Thelohau, 

 viz, sporoblast segmentation, number of nuclei, etc. 



Development of capsule: A peculiar arrangement, believed to be 

 connected with the development of the capsule, was noted, viz : often in 

 the body of the sporoblast, near the nucleus, a clear rounded space, into 

 which a small protoplasmic button projects. This observation is, how- 

 ever, a vexy delicate one, and the figures are slightly diagrammatic. 



Morphology of the sporophorons vesicles. — The constitution and develop- 

 ment of the spore-producing vesicles permit us to consider them only as 

 the morphological equivalent of the pansporoblasts of the other Myxo- 

 sporidia. These octosporophorous pansporoblasts form a transition 

 from the oligosporogenetic pansporoblasts of the larger species to the 

 polysporogenetic pansporoblasts of Glugea, which latter produce a con- 

 siderable and inconstant number of spores. Above all, one fact is here 

 to be noted, viz, the entire absence of a mj^xosporidium. No structure 

 whatever could be detected which could be regarded as its morpho- 

 logical or physiological equivalent. 



But whence come these spore-producing vesicles ? Evidently they do 

 not represent the first stage of development. Now if, as is usual, they 

 are formed in the interior of a protoplasmic mass, what has become of 

 the latter? In all other known species a considerable protoplasmic 

 residue remains, even of myxosporidia whose development is completed, 

 and in which young pansporoblasts are no longer to be found, but only 

 entirely mature spores. But here are young pauspoi'oblasts at their 

 simplest (uninucleate spherules) with not the slighest trace of a sur- 

 rounding protoplasm. As long as we had only found these organisms 

 in the mature state (as sporophorons vesicles) that absence might have 

 been explained, in case of necessity, on the supposition of a complete 

 previous transformation of the myxosporidium into pansporoblasts, the 

 myxosporidium vanishing in the process or leaving only insignificant 

 vestiges. But in the presence of the now known earlier phases of 

 development this hypothesis seems hardly admissible. 



