218 REPORT OP THE COMMISRK^NKR OF FISH AND FISHERIES. 



.Vyxosporldiiim. — Myxospoiidiuin usually showing- no clear dilfercn- 

 tiation of ectoplasm and oiuloplasni cx((>pt iu thin sections, wlieie certain 

 jwrtious exhibit very plainly a tolerably thick, i^riwiule-free exteiior 

 zone, possessing' a great interest on account of its very distinct line 

 radiate striation. Riidoi)lasiii thickly studded with very small but 

 distinct nuclei which in thin sections are, even in the fresh state, rather 

 plainly visible as faint roundish corpuscles, in which dilute acetic acid 

 ditlfercntiates a dark somewhat granulated membrane, a small dark 

 nucleolus, and, sometimes quite clearly, fine nuclear threads radiating 

 from the nucleolus to the membrane. This structure, together with 

 their intense affinity for stains, perniits no doubt as to their nuclear 

 nature. 



Spore formation.^ — This species never shows a paired spore-devrlop- 

 ment, or a development within a pansporoblast ("?; see below), the 

 spores being directly imbedded in the endoplasm. These spores, how- 

 ever, show indications of a similarity in their development to the other 

 MyxosporkUa in their origin from a trisegmented ("trinucleate") plasma- 

 globule, 2 of whose segments develop the capsules and the third the 

 sporoplasm. 



Development of spore? — In the myxosporidium, inclosed in a delicate 

 membrane, a number of mature spores are seen, many things pointing 

 to their origin from the proto])lasm. They always contain o pale, 

 almost spherical, but somewhat angular bodies. The membrane fre- 

 quently shows an excavation and an opening at one end. At this end 

 the 2 protocysts are situated, the protosporoplaam being remote there- 

 from. Further observation shows the protosporoplasm to de\ elop into 

 the sporoplasm of the mature spore and the two protocysts to give 

 origin to the capsules. The latter structures develop within the proto- 

 cysts, the filament appearing first in the extruded condition, apparently 

 forming a prolongation of the capsular wall. 



Subsequently, in the light of his observations on the development of 

 Myxidium licberlcuhnii, Biitschli inclined to interpret thus: That the 3 

 spheres (viz, the 2 protocysts and the protospuropla&m) represent 

 not plasma-spheres but nuclei, the latter being, on this supposition, 

 imbedded in a plasma mass which he had failed to see, probably on 

 account of strong swelling and great transparency. 



The observations of Balbiaui and of Th(51ohan, however, render it 

 almost certain that Biitschli's observations were accurate and that his 

 subsequent interpretation was erroneous (see also pp. 82, 223). Upon 

 this view the present species would seem to develop pansporoblasts, 

 eacli with a single spore. 



Spore. — Lenticular-oval, anterior end sharpened, showing quite plainly 

 a shallow funnel-shaped depression; posterior end rounded off; dimen- 

 sions 10 to 12 ;u by 9 to 11 /<. On vertical view, contour rather variable, 



'Butschli, 1882, Broun's Tliier-Reich,!, p. 597. 



*The description is Biitschli's (Ztschr. f. wies. Zool., 1881, xxxv, pp. 64G-8). 



