Miscellaneous, 197 



The llistorij of the FreshwaUr JS'i'inerteans ; their Geographiad 

 Distribution and their Orif/in. By M. Jtjles de Guerne. 



A learned Swiss naturalist, Dr. du Plcssis, recently auiiounced, 

 in one of the most widely circulating zoological journals *, that he 

 had just made a very surprising discovery. On the2i)th of October, 

 1891, a Neraertean had been found by him on the shores of the 

 Lake of Geneva. " The presence of this marine ivorm tvas so 

 imjrrobable,'' says the author, " that ive coidd not believe our exjesT 



However curious the fact mentioned by Dr. du Plessis may appear, 

 it is nevertheless not new. Nemerteans have been observed in 

 fresh water sufficiently often that their existence out of the sea 

 ought nowadays to be no longer a matter of great surprise f- Prof. 

 Vaillant has already reminded us, in the very periodical in which 

 Dr. du Plessis's article appeared, of several analogous cases which 

 have been known for a very long time +. 



In reverting to the question myself I do so in the first place in 

 order to supplement M. Vaillant's note, in which divers remarkable 

 cases seem to have been overlooked, and secondly and in particular 

 in order to call the attention of French naturalists to the freshwater 

 Jfemerteans which may very well happen to come into their hands. 



As a matter of fact these animals were discovered in France, in 

 the neighbourhood of Montpellier, by Duges, who described and 

 figured them as early as 1828 §. 



Prof. Yaillant appears to have met with these worms once more 

 in the same region some fifteen years ago ||. However, since he 

 did not study them in any way, and the writings of Dugcs, which 

 are already antiquated, are very incomplete, there remains some 

 doubt as to the value and identity of the species. 



Be that as it may, the first precise statements as to a freshwater 

 Nemertean were made in 1847 by de Quatrefages, who called the 

 creature LWia Dagesi. Tlie animal actually occurred in Paris, in 

 the Saint-Martin Canal, and if we can hardly hope to rediscover it 

 in this medium, which is nowadays polluted by all sorts of impuri- 

 ties, we can at any rate look for it in certain more limpid waters of 

 the basin of the Seine. Three figures accompany the description of 

 PoJia Dagesi, the discovery of which certainly passed unnoticed 

 owing to its being published in the ' Recherches anatomi(|ues et 

 zoologiques faites pendant un voyage sur les cotes de Sicile ' *\\. 



* ' Zoologischer Anzeiger,' Bd. xv. no. 384, Feb. 15, 1892. 



t The small size of the animals is probably one of the reasons which 

 prevents their being recognized. They are tiliform, and scarcely exceed 

 15 millim. in length when extended. 



X Zool. Anzeiger, Bd. xv. no. 387, March 28, 1802. 



§ Ann. des Sc. uat. vol. xv. (1828), and vol. xxi. (1830). Duges 

 created for these worms the genus Prostcnna, the type of which is P. clep- 

 sinoides, found in running water under stones (1828). Later on three 

 other species (P. lumbrtcoideuni, P. candidum, and P. armntum) were 

 added. Of the latter the first alone is fluviatile ; the two others were 

 found on the shores of the Mediterranean (1830). 



II Hist. uat. des Auneles mar. et d'eau douce, vol. iii. (1889). 



^ 2* partie, note on page 211, iu the explanation of the plates. The 

 figures concerning Pvlia J)uf/esi are to be found iu pi. xiii, under the 

 numbers 11, 12, and 13. 



