136 MOUNTAIN AND MOORLAND 



water polyps, by the freshwater sponge and many 

 unicellular Protozoa and by other members of a 

 very representative fauna. 



The open water of the lake is peopled by a plankton 

 of Infusorians, Wheel Animalcules, Water Fleas, 

 Water Mites, and a few swimming larvae of insects 

 and molluscs. "In the transparency, the delicacy of 

 build, and the occasional presence of long processes 

 believed to be useful in drifting we see adaptations 

 to the open water life." 



The third set of animals in a lake are those that 

 live at great depths, which reach a maximum in Lake 

 Baikal viz., 760 fathoms. The floor of a deep lake is 

 "a region of uniformity, where there is neither day 

 nor night, where the temperature is low and relatively 

 uniform, where the pressure is very great, where there 

 are no movements apart from life, and where there is 

 usually much mud." Since it is dark in very deep 

 water, there are practically no plants except Bacteria 

 and the like, though the floor of the lake is rich in 

 green and blue-green Algae to the limit of illumination. 

 The deep-lake animals include some unicellulars, 

 various kinds of simple worms, some red-blooded 

 worms, various Crustaceans, insect larvae and Water 

 Mites, and a few molluscs. " Finally, there are a few 

 fishes like the giant Silurus and its small counterpart 

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

 of the young stages of a formidable human tapeworm 

 called Bothrlocephalus latus, thus linking up the dark 

 depths of the lake into connection with human life." 



In an introductory study it is not very profitable to 

 give lists of plants and animals in different haunts, but 

 examples are necessary in order to give definiteness 



