. Animal life as affected by the natural conditions of existence. Animal ecology. 148 THE INFLUENCE OF INANIMATE SCKEODNDINGS. by a rapid stream of pure drinkable fresh-water, and opened their shells to it. Many marine Bryozoa occur also in fresh water. Among the Annelida the case seems to be rarer, and I have only been able to find one instance mentioned in books by Leidy, who discovered a worm, Manayunkia, belonging to the Cephalobranchiata, in the Schuylkill River, near Philadelphia. The Nemertino worms, so common in the sea, have only one representative in fresh water of certainly a very d

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. Animal life as affected by the natural conditions of existence. Animal ecology. 148 THE INFLUENCE OF INANIMATE SCKEODNDINGS. by a rapid stream of pure drinkable fresh-water, and opened their shells to it. Many marine Bryozoa occur also in fresh water. Among the Annelida the case seems to be rarer, and I have only been able to find one instance mentioned in books by Leidy, who discovered a worm, Manayunkia, belonging to the Cephalobranchiata, in the Schuylkill River, near Philadelphia. The Nemertino worms, so common in the sea, have only one representative in fresh water of certainly a very d
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Image ID: RDJGWP
. Animal life as affected by the natural conditions of existence. Animal ecology. 148 THE INFLUENCE OF INANIMATE SCKEODNDINGS. by a rapid stream of pure drinkable fresh-water, and opened their shells to it. Many marine Bryozoa occur also in fresh water. Among the Annelida the case seems to be rarer, and I have only been able to find one instance mentioned in books by Leidy, who discovered a worm, Manayunkia, belonging to the Cephalobranchiata, in the Schuylkill River, near Philadelphia. The Nemertino worms, so common in the sea, have only one representative in fresh water of certainly a very divergent form; of Sponges we find only one genus, Spongilla ; of the Hydroids only two, Hydra and Cordylophbra (fig. 40), which, in the course of time, have become true fresh-water animals.^*. Via. 39,—Oyster from the Cumalaran RiTer at Basilan (south of Mindanao) ; it lives in spots where the" water is quite fresh. C. The effect of the different percentage of salt in the water.—The cases adduced above prove that it is often impos- sible to distinguish, by systematic characters alone, whether an animal is fresh-water or marine, since there ars many species in fresh water whose nearest allies live in the sea, and vice versa. Theoretically, then, we must admit that there is no general and insuperable impossibility that they should exchange their life in one medium for that in the other. But this theoretical possibility is not, so far as we know, universally practical; for whole groups—as the Brachiopoda, Sipunculidae, and Echinodermata—have hitherbo been found only in the sea. The question now is : "What causes have prevented or still pre- vent a transfer of marine animals from sea-water to fresh. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original work.. Semper, C. (Carl), 1832-1893. New York, D. Apple

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