THE HAUNTS OF LIFE 105 



much mud. It is the least populous region. Since it is 

 dark, there are practically no plants except Bacteria and 

 the like. The animal population includes Amoebae and 

 their relatives (e.g. species of Difflugia and Arcella), 

 Infusorians like Stentor and Vorticella, a deep-water reddish 

 Hydra, simple Turbellarian and Nematode worms, others 

 of higher degree hke Nais, some species of Fredericella 

 and Pahidicella among Polyzoa, a number of Crustaceans 

 (e.g. blind species of Cyclops and Asellus), some insect 

 larvae, e.g. of the harlequin fly, a few water-mites hke 

 Hygrobates, a few molluscs hke the bivalve Pisidium 

 hoferi and the Gastropod Limncea abyssicola, and finally 

 a few fishes hke the giant Silurus and its small counterpart, 

 the burbot (Lota vulgaris), which is one of the hosts of the 

 young stages of the formidable human tapeworm (Bothrio- 

 cefhalus latus), thus hnking up the dark depths of the lake 

 into connexion with human life. 



In regard to other freshwaters, such as ponds and rivers, 

 it must suffice to say that each has its distinctive fauna, 

 and that the population in rivers is much less abundant 

 than elsewhere. In the actual current of the Rhine, 

 Lauterborn found only twenty Rotifers, two Crustaceans, 

 nine Protozoa, and two Diatoms ; but of course this number 

 is greatly increased when we take account of the creatures 

 — e.g. larval insects — ^that creep about on the stones and 

 among the weed. Wherever there is stagnancy, e.g. in 

 the pools of the overflow bed, we find much the same 

 fauna as in ponds. As to ponds, while there are a few 

 forms, e.g. Leptodora hyalirpa, which occur both in ponds 

 and lakes, the fauna of the shallow pond is usually quite 

 different from that of a true lake. Thus no one expects to 

 find a Crustacean like Byotrephes hngimanus in a pond. 



