POLYZOA OF VVATEKWORKS. 439 



oases, tliis is no doubt due to the fact that that time of yeai^ 

 is the period at which the tubes of Polyzoa naturally disin- 

 tegrate, with the result that branches are set free and clioke 

 the meters. 



(4) 



At the end of October 1912 I received, through Mr. S. C. 

 Chapman, a sample from an English waterworks installation, the 

 locality of which I am not permitted to mention. It consisted, 

 in the main, of a mass of tubes of Paludicella articulata. The 

 polypides had already disappeared owing to the lateness of the 

 season ; but the sample was a particularly beautiful specimen, 

 covered with a profusion of hibernacula or winter-buds, which 

 were developed on every branch. Among the branches of the 

 Paludicella there were disintegrated fragments of Fredericella 

 sultana, Mr. Chapman informs me that serious trouble had been 

 experienced for some time at the locality in question, although 

 the nature of the organisms causing it had not been recognized. 



(5) Aberdeen. 



At the end of March, in the present year, I received a sample, 

 very similar to the last one, fi'om the Aberdeen Waterworks, 

 again through the kindness of Mr. Chapman. This consisted 

 principally of a tangled mass of Paludicella articulata,, composed 

 of empty zocecia bearing numerous hibernacula. The sample 

 also included a few pieces of Sjiongilla lacustris (determined by 

 Mr. R. Kirkpatrick), crowded with gemmules, a few young speci- 

 mens of Limncea peregra (determined by Mr. G. C. Robson), and 

 some Dipterous larvae. These were referred by Mr. F. W. 

 Edwards to a species of Chironomus, which was, however, not 

 the same as the species found at Torquay. There were also a 

 number of tubes, formed of cemented mud, which appear to 

 have belonged to the Ch,i7'oiiomus-liirvse. 



The following case may also be mentioned, because, although 

 not illustrating the occurrence of Polyzoa in waterworks, it has 

 an obvious bearing on the importance of filtration : — 



(6) Hampton-on-Thames. 



On May 22, 1912, ' The Daily Mail' published a short account 

 of the occurrence of enormous numbers of " freshwater mussels " 

 in a 36-inch water main at Hampton-on-Thames. It was stated 

 that 90 tons of these animals had been removed from a length of 

 a quarter of a mile of this main, the diameter of which had been 

 reduced by them from 36 inches to 9 inches. The " mussels " 

 were examined by Mr. G. 0. Robson, who found them to belong 

 to Dreissensia j^o^y^'f'Orpha, a Lamellibranch which has been 

 recorded in the pipes of the Hamburg water-suj)ply and elsewhere. 

 Mr. H. B. W. Stent, A.M.Inst.C.E., the Resident Engineer of 



