. Ecological animal geography; an authorized, rewritten edition based on Tiergeographie auf ockologischer grundlage . Fig. 97.—a, Limnaea stagnalis var. bodamica from moving water; b, L. stagnalis from quiet water, normal to the arrow, beyond which the shell is weighted with cement, producing growth similar to a (after Voigt); c, L. stagnalis from a pond, the growth form produced by a strong growth of fila- mentous algae on the shell, which hinders its motion. X 2/3. wise are black (Polycelis nigra, Planaria alpina) are represented by pale yellow forms in the depths of the lakes in the Alpine
. Ecological animal geography; an authorized, rewritten edition based on Tiergeographie auf ockologischer grundlage . Fig. 97.—a, Limnaea stagnalis var. bodamica from moving water; b, L. stagnalis from quiet water, normal to the arrow, beyond which the shell is weighted with cement, producing growth similar to a (after Voigt); c, L. stagnalis from a pond, the growth form produced by a strong growth of fila- mentous algae on the shell, which hinders its motion. X 2/3. wise are black (Polycelis nigra, Planaria alpina) are represented by pale yellow forms in the depths of the lakes in the Alpine foothills. The temperature is very constant in the deeper pedon as compared with that of the littoral region. In the Lake of Lucerne the tempera- ture at depths of 30 to 200 m. is not less than ° and not more than 10°; the variation at depths of 100-200 m. is only about 1°.20 Steno- thermal animals, adapted to the cold, with a few eurythermal forms, find a favorable habitat in the greater depths. There is no marked movement of water at greater depths. Because of this the floor is evenly covered with fine mud varying according to its origin, which is usually organic. The dead bodies of plants and animals which live in the open water, the excrements of fishes, and the products of disintegration of shore plants sink to the bottom and form a layer of detritus which becomes the food of innumerable mussels (Pisidium), slimeworms (Tubificidae), and bloodworms (Chirono- midae). These continually engulf the mud and give off small mud-balls
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Keywords: ., bookcentury1900, bookcollectionbiodive, booksubjectanimalecology
