. Animal life as affected by the natural conditions of existence. Animal ecology. 124 THE INFLUENCE OF INANIMATE SUEROUNDINGS. thenogenesis were not exposed to the effect of cold, but kept in a constant summer heat, and at the same time supplied with suitable food, no males would occur, and the young would be' uninterruptedly produced by the parthenogenetic mode. In fact Reaumur did succeed in this way in producing artificially above fifty parthenogenetic generations in the course of three or four years, all descended from one mother. The converse ex- periment has never, so far as I know, been
. Animal life as affected by the natural conditions of existence. Animal ecology. 124 THE INFLUENCE OF INANIMATE SUEROUNDINGS. thenogenesis were not exposed to the effect of cold, but kept in a constant summer heat, and at the same time supplied with suitable food, no males would occur, and the young would be' uninterruptedly produced by the parthenogenetic mode. In fact Reaumur did succeed in this way in producing artificially above fifty parthenogenetic generations in the course of three or four years, all descended from one mother. The converse ex- periment has never, so far as I know, been made—namely, whether it would be possible to produce males in the spring by. Fig. 31.— a, Diplozoon paradoxum, from the gill of a fresh-water fish ; b, Polystomum iniegerrimum, from the bladder of a frog. artificially lowering the temperature, although they do not pro- perly appear till later in the year, and thus to diminish the normal number of successive parthenogenetic generations in a summer. It is highly probable that it might succeed. The facts lately communicated by Zeller are no less interest- ing. He found that certain parasites, in precise opposition to the Aphides we have been speaking of, Diplozodn paradoxum and Polystomum integerrimum (fig. 31), produce true eggs in the summer only, which must be fertilised before they can. 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 Semper, C. (Carl), 1832-1893. New York, D. Appleton and Co.
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