ABSTRACT
About two years ago, while examining some sections of a Nereis (probably N. diversicolor, O. F. Müll.) which I had cut in the Zoological Laboratory at University College, London, I discovered an interesting organ, which appears to have hitherto escaped the notice of those naturalists who have studied the anatomy of the Nereids. Since then I have from time to time continued my observations, both in London and in the Oxford Museum, always hoping to be able to obtain the stages in the development of Nereis, the study of which alone can give a real clue to the homology and functions of these organs. This unfortunately has not been possible, owing chiefly to the fact that I have not been able to go myself to the sea-side to pursue my researches. It has therefore been thought advisable to publish the facts as they stand, and this paper amounts to little more than a mere description of this new organ. Some notes on the minute structure of the nephridium of the Nereids have also been added.
I am much indebted to Signor Lo Bianco, of the Naples Zool. Station, for collecting and sending me several species of Nereis.
I hope soon to be able to give a description of the minute structure of the nephridia of some of the genera mentioned above.
Should future observations establish the fact that the dorsal ciliated organ is a genital duet, it might well be compared with the metameric genital canals of the Nemertines.
Not only is the alimentary canal much reduced (according to Claparéde [2] the Heteronereids take no food), but the nephridia also seem to be degenerate and in some cases even absent. I have not, however, yet been able to examine sufficient material to say anything definite on this latter point.
Since this was printed I have found that E. Meyer put forth very much the same theory in 1890 (“Die Abstammung der Anneliden,” ‘Biol. Central.,’ x).
