428 DR. S, F. UAUMER ON THE 



recorded Vivipara (Pcdudina), Anodonta and Unio. Planarians 

 and a JSTemertine (Tetrastemma) were also found, although the 

 method employed for collecting the samples was not well adapted 

 for the discovery of the smaller organisms. Rotifers and Infusoria 

 {Vo7~ticeUa, Stentor, ParaTiiecmniii, and Acineta) were, however, 

 discovered. 



Even the Vertebrates were not unrepresented in this remark- 

 able fauna. The Eel, up to a foot in length, was common. As 

 many as six individuals were sometimes present in one sample, 

 and Kraepelin estimated that there must have been many 

 thousands in the system. Other fishes were less numerous; 

 but the Stickleback {Gasterosteus aculeatus) was occasionally 

 found ; and on one occasion a Burbot {Lota vidgaris), a foot in 

 length, was discovered. A young Flounder, sevei'al centimetres 

 long, was found in company with the Prawn [Leander) above 

 alluded to. 



Summarizing his observations, Kraepelin points out that the 

 constituents of the fauna of the water-pipes consist almost exclu- 

 sively of forms which feed either on detritus or on one another ; 

 that in the absence of ordinary green plants, forms which feed on 

 these are absent ; while animals like insects, which require access 

 to air, are also absent. For the species which had succeeded in 

 adapting themselves to their novel environment the conditions 

 were, on the contrary, exceptionally favourable, and indeed more 

 favourable than those found normally in Nature. Some of the 

 fa,ctors specially alluded to, in this connexion, were the absence 

 of carnivorous insects, and the existence of large surfaces suitable 

 for the attachment of sessile animals. 



Kraepelin proceeds to consider the ultimate source of the food 

 of the pipe-fauna ; and he points out that this must consist of 

 the microscopic organisms and other detritus introduced into the 

 system by the constant flow of water from the Elbe. The absence 

 of any filtering arrangements, at that time, allowed these particles 

 to enter without hindrance. In working vip these materials into 

 new organic substances the Polyzoa played a part of pre-eminent 

 importance ; particularly since these animals formed so large a 

 proportion of the entire fauna. The carnivorous animals natur- 

 ally depended for their supply of food on the organisms which 

 were able to make use of the microscopic detritus. Kraepelin 

 accoi'dingly arrived at the perfectly legitimate conclusion that if 

 the food- supply were to be cut off by the introduction of an 

 efficient filtering arrangement, the pipe-fauna would before long 

 die out. The soundness of this conclusion was amply demon- 

 strated by the cessation of the trouble at Hamburg on the 

 introduction of the remedy suggested ; while the experience of 

 Water -Engineers in many other places has been of a similar 

 nature. 



The presence of Polyzoa in water-pipes is, however, not an 

 unmixed evil ; since, as has been pointed out by several obseivers, 

 if floating organisms exist in the water, the Polyzoa serve the 



