Since the adoption of an aquatic mode of life by Desis and Argyroneta involves no increased facilities in getting food, and merely substitutes for ordinary terrestrial enemies fishes and crustaceans in the former case, and fishes, amphibians, and insectivorous water-insects in the latter, the supposition is justified that the change in environment is due to the unremitting persecution of Pompilidae and Ichneumonidae, which would not venture to pursue their prey beneath the water's surface.
Animals of the next higher order, the amphibians of the coal measures and the Permian, were first comprehensively treated in the masterly memoirs of Christian Erich Hermann von Meyer (1801-1869) beginning in 1829, especially in his Beitrage zur Petrefactenkunde (1829-1830) and his Zur Fauna der Vorwelt (4 vols., 1845-1860).
New and unheard-of orders of amphibians, reptiles and mammals came to the surface of knowledge, revolutionizing thought, demonstrating the evolution theory, and solving some of the most important problems of descent.
Illustrations of this law were set forth by Cope as early as 1861 (see " Origin of Genera," reprinted in the Origin of the Fittest, pp. 95 -106) in pointing out the extraordinary parallelisms between unrelated groups of amphibians, reptiles and mammals.
In fishes and amphibians the organ consists of right and left lobes, and a gall-bladder is present.
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