BLOOD-PABASITES OF FISHES OCCURRING AT ROVIGNO. 143 



(17) lias recently described the nuclear structure in certain 

 developmental forms of a ti'ypanosome occurring in Pontob- 

 della, which trypanosome she regards (and we think correctly) 

 as T. raiae. Our own observations quite agree with her 

 account; we are able, perhaps, to add a few more details 

 with regard to the karyosomatic mass. (Our main purpose, 

 as we have already said, is to emphasise the contrast between 

 this type of nucleus and that of a hfemogregarine.) 



The nucleus is very generally oval in shape and always 

 possesses a well-defined, regular contour. Its size varies not 

 inconsiderably (cf. figs. 52-56), and, as might be expected, is 

 in accordance with the size of the parasite, small- or inter- 

 mediate-sized individuals having a smaller nucleus than the 

 large ones. The size may be as small as 2'4^ by 1'7/j, or as 

 large as S'ljn by 2'6 ^, The greater part of the nucleus is 

 occupied by aprominent deep-staining body — the karyosomatic 

 mass. Around this appears a practically clear space, which 

 is bordered or limited by a sharply marked line, the nuclear 

 membrane. Any space or halo surrounding this on the outside 

 again, as sometimes occurs (cf. figs. 52 and 54), is most likely 

 a shrinkage-space. Delicate rays, sometimes four or five in 

 number, sometimes more, pi'oceed from the central mass to 

 the membrane; these are usually very faintly stained, but 

 can be made out with a good illumination, especially in iron- 

 hfematoxylin preparations. Both membrane and rays are 

 always green after Twort (figs. 66, 67, 68a). Hence we may 

 regard them as achromatic in structure. The rays are pro- 

 bably comparable to a linin framework for the support of 

 the karyosome. The membrane is a much more definite 

 structure than in the case of the hsemogregariue-nucleus. 

 In this parasite both membrane and rays appear to be, as a 

 whole, remai-kably free from chromatin, very different in this 

 respect from the chromatic reticulum of the hfemogregarine. 

 The only possible indications of chromatin are furnished by 

 small dots or condensations at the junctions of the rays with 

 the membrane; they are best seen in iron-haematoxylin pre- 

 parations (fig. 54). We can get no evidence of a red colour 



