certain Species q/'^olosoma. 263 



is confined to the terms used bj the authors in their several 

 descriptions. 



I can confirm the statement of Vejdovsky tliat there is no 

 nucleus in the cells containing the coloured oil-globules ; so 

 far this species agrees with 2Eolosorna Ileadleyi and differs 

 from j^olosoma tenehrarum^ where a nucleus appears to be 

 invariably present in the fully mature cell. 



I rei'er the present species to ^olosoma quaternarium on 

 account of the fact that there are no nephridia in the oesoplia- 

 geal segment ; they begin, in fact, in the second seta-bearing 

 segment. But I cannot agree with Vejdovsky {loc. cit. p. 20j 

 that the pigment-spots are less numerous upon the prostomium 

 than elsewhere ; 1 find considerable variation in this parti- 

 cular, but in many specimens — I rather think in the majority 

 — the oil-globules were quite crowded in the lateral regions of 

 the prostomium. 



I have just mentioned the fact that the oil-globules of this 

 species, like those of yEolosoma Ileadleyi and unlike those of 

 JflolosMfM tenehrarum^ are not surrounded by any cell-proto- 

 plasm or nucleus, except of course when they are just 

 beginning to be formed; correlated with this is the fact that 

 on treatment with iodine solution there is no deposition of 

 black granules around the coloured oil-globules ; this miglit 

 perhaps be expected to occur in the periphery of the smaller 

 oil- globules, but it does not. The absence therefore of this 

 reaction, which is so characteristic of ^olosoma tenehrarnmj 

 may perhaps not necessarily indicate a profound difference in 

 the pigment of the three species, jEolosorna quaternarium, 

 varieffaturn, and Headleyt, as compared with ^olosoma tene- 

 hraruTii. If the explanation which I offered in my paper 

 upon ^olosoma tenehraram (Proc. Zool. Soc. 1889, p. 6'i) 

 of the black stain jn'oduced by iodine be correct, viz. that it 

 is a precipitation of elemental iodine caused in some way by 

 the coloured oil-globule, it is perhaps a little difficult to see 

 why the supposed influence of the coloured oil-drop in jEoIo- 

 sorna quaternarium does not reach the cells immediately sur- 

 rounding it with which the oil-globule is so nearly in contact. 

 This theory may of course be wrong ; but in the meantime 

 it seems to me to be on the whole more probable that there is 

 so far a difierence between the several pigments, and that the 

 orange-brown pigment of jEolosorna quaternarium and the 

 bright green pigment of jEolosoma variegatum and Ileadleyi 

 may be less perfect as respiratory pigments, and therefore 

 in course of degeneration. In this connexion it is interesting 

 to note that ^olosoma tenelyraruin is on a decidedly higher 

 level of organization than any of the other species at present 



