Über das Auftreten einer erheblichen Schalenabweichung bei einer Posthornschnecke
During a period of high temperature in January 1948 several specimens of Anisus (Anisus) leucostoma Millet, belonging to the snail family of Planorbidae, were obtained in the still fairly cold water, and brought into a water tank in the warm laboratory. There they soon began to breed. All those secured had normally developed shells (fig. 1); the same applied to the snails found later at the habitat. Amongst young normal snails of the generation bred in the tank, 17 specimens with abnormally coiled shells were found; they appeared together at the same time and were originally of the same size. They grew; but only 9 reached maturity. The oldest ones lived for 8 months. The shells were sinistral as those of the parent generation, but very different in shape, due to the fact that they were scalarids (Hg. 2-3). In July 1948 some egg capsules were found in the tank of the abnormal animals; these capsules were slightly smaller than usual and contained 8 eggs at the maximum. Young snails hatched; but the last of these died at the end of November 1948, not having reached maturity. The shape of the shell was about the same as that of their abnormal parents, probably slightly more irregular (fig.4). It is obvious that this variation in the shell is an hereditary one. It is considered that the transfer from the natural cold water to the warm temperature of the laboratory caused a type of shock to the animals and probably effected the mutation.
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