4H INFLUENCES OF CULTIVATION 



throughout the entire water system. It is impossible to 

 detail the species of the fifty distinct genera of creatures 

 thus captured. Eels were common, sometimes as many 

 as six in a single sample, so that the investigator 

 estimated that thousands must have been present in the 

 system. Sticklebacks, a Flounder, and a Burbot were en- 

 trapped. Living shell-fish were frequent; not only the fresh- 

 water Pond Snails, but even species of much larger Freshwater 

 Mussels. Worms were common, and some of the smaller 

 Leeches were present "in almost incredibly large numbers." 

 The water was peopled by swimming Crustacea Water-fleas, 

 the Freshwater Shrimp, and such like and in almost every 

 sample, hundreds, even thousands, of the Freshwater Slater 

 (Asellus aquaticus] were found "in ugly crowds." The 

 attached, inactive inhabitants of the water-pipes were even 

 more numerous and of more economic importance than this 

 enormous army of active swimming organisms. A Fresh- 

 water Sponge and a Hydroid Zoophyte were common; but 

 more serious were the growths of " Leitungsmoos " plant- 

 like colonies of animal moss or Polyzoa, which in Antwerp 

 were found to form all round the inside of a 60 cm. 

 (about 24 inch) pipe a coat nearly 10 cm. (over 4 inches) 

 thick. From about 220 yards of this pipe, two cart loads of 

 the animal obstruction were removed. 



Other cities, even if they yield first place to Hamburg, 

 have still sufficiently remarkable water-pipe faunas. From 

 the water-conduits of Paris, there were described in 1913 no 

 less than forty-four species of molluscan shell-fish alone; in 

 Ypres (before the War), Dr A. Kemna found that the opening 

 of a hydrant was a signal for the appearance of masses of 

 shells, Polyzoa, and Worms in the jet of water. 



Britain also has its waterworks' faunas. In 1910 the 

 irregularity of the Torquay water supply and the choking of 

 taps and meter strainers, led to the discovery that the mains 

 in every part of the district of supply were coated and 

 choked with living growths of the Polyzoon, Plumatella 

 emarginata. Freshwater Sponges (Spongilla lacustris] have 

 been found growing in luxuriance in the pipes of Cardiff 

 waterworks. Eleven species of Mollusca have been recorded 

 from a water-main at Poplar, and 90 tons of the introduced 

 Zebra Mussel (Dreissensia polymorpha) (Fig. 68) are said to 



