Ecological animal geography; an authorized, Ecological animal geography; an authorized, rewritten edition based on Tiergeographie auf ockologischer grundlage ecologicalanimal00hess Year: 1937 372 ANIMALS IN INLAND WATERS Rotifers are also quite numerous. Of crustaceans, Artemia is a salt-water inhabitant of world-wide distribution, which usually occurs in great numbers. Resting stages, in all these forms, can survive periods of increased concentration; thus the Protozoa have cysts and the rotifers and Artemia have hard-shelled winter eggs. This is an important point in their adapta
Ecological animal geography; an authorized, Ecological animal geography; an authorized, rewritten edition based on Tiergeographie auf ockologischer grundlage ecologicalanimal00hess Year: 1937 372 ANIMALS IN INLAND WATERS Rotifers are also quite numerous. Of crustaceans, Artemia is a salt-water inhabitant of world-wide distribution, which usually occurs in great numbers. Resting stages, in all these forms, can survive periods of increased concentration; thus the Protozoa have cysts and the rotifers and Artemia have hard-shelled winter eggs. This is an important point in their adaptation to their environment. The winter eggs of Artemia, like those of other Euphyllopoda, are very resistant; they may develop even after a period of 8 years of Artemia is very variable in its appearance; every habitat has its own form which can be distinguished by color, size, location and num- a Fia. 108.—Caudal fork of Artemia salina from waters of varying salt content, near Odessa: a, from water of 8°; b, 14°; c, and d, 18°; e, °; and /, 25° Baume. After Schmankewitsch. ber of setae, form of the posterior end, etc. A large number of these changes are due to the influence of the salt content;43 since this is constantly changing in nature, reliable information concerning these phenomena can be obtained only by breeding experiments in water of constant concentration. With an increase of salt content the animals become smaller, the length of the narrow post-abdomen in comparison with the abdomen increases, the furca (tail fork) becomes shorter and is set with fewer hairs (Fig. 108). The appearance of males also varies with the habitat; in many places there are only females, in others both sexes. One copepod, Diaptomus salinus, is also rather resistant against fluctuations of salt concentration; this is rare in fresh water, but may be abundant in salt lakes such as Lake Aral. Insects and insect larvae are the most numerous among Metazoa. A number of gener
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