POLYZOA OF WATERWORKS. 427 



light had, of coui^se, no access; and by the further consideration 

 that he might be able to detect some modifications of structure, 

 as compared with the ordinary inhabitants of the Elbe, in the 

 animals which were living under these unusual conditions. 

 Although the results of the investigation were not of the nature 

 which he had anticipated as possible, they were nevertheless very 

 surprising ; since he was able to demonstrate that some fifty 

 genera of animals occurred, often in enormous numbers, in the 

 system. The examination was made with the assistance of a 

 specially devised piece of apparatus which was screwed on to 

 various parts of the water-mains. A column of water was 

 allowed to escape through this arrangement, and the animals 

 which were contained in it were filtered off. The results obtained 

 were very uniform, in whatever part of the system the apparatus 

 was used, so that it became clear that the organisms fovind were 

 not merely a fortuitous collection of individuals which had acci- 

 dentally been introduced into the supply, but were, on the 

 contrary, perfectly normal constituents of a definite faiuia in- 

 habiting the water-pipes under a pressure of 2|-5;i atmospheres. 

 Among these organisms a conspicuous, and usually the greater, 

 part consisted of large masses of what had become known to the 

 workmen as " Leitungsmoos " — a mass of entangled tubes which 

 belonged principally to Polyzoa of the genera Fredericella, Fluma- 

 tella and Fcdudicella, but partly to the well-known Hydroid 

 Cordylophora. Sponges (Ephpdatia JiuviatiUs and Spongilla 

 lacust7-is) were frequently found. Colourless forms of Hydra 

 were discovered; but, as might have been expected, ILviridas 

 appeared to be completely absent. Several species of Freshwater 

 Oligochsetes were recorded, as well as " almost incredibly large 

 numbers" of Leeches {Glossiphonia and Nephelis). Parasitic 

 worms M^ere represented by Echinorhynchus^ found in large 

 numbers, in its larval condition, in Asellus; and, in its adult 

 condition, apparently derived from Eels. Among the Polyzoa 

 the " mossy " appearance of the masses of tubes above alluded to 

 was generally due to Fredericella sidtana. Traces of Fcdudicella 

 articidcda were generally found : wdiile Flumatella was represented 

 principally by a foi'm described by Kraepelin as F. princeps, var. 

 viuscosa, and by the Alcyonelloid F. fungosa. Almost every 

 sample contained hundreds, or indeed thousands, of Asellus 

 aqucdicus, which were found creeping over the Polyzoa " in ngly 

 crowds." The Freshwater Shrimp, Gammarus pidex, was some- 

 what less numerous, while various forms of Cladocera, Copepoda, 

 and Ostracoda were nearly always present. Leander \Palcemo')i\ 

 squilla and Mysis chamceleon were represented by single finds. A 

 small water-mite and a few Dipteious larvse and pupte were rarely 

 met with. 



Among Molluscs the commonest species was Dreissensia, poly- 

 morpha ; but Bithynia tentacidaUt was frequent, and othei- fresh- 

 water genera — Fhysa, Limncea, Flanorhis, Ancyhis, and Sphceriimi 

 (Cyclas) — were also discovered; while Petersen had previously 



