. The Biological bulletin. Biology; Zoology; Marine biology. GROWTH AND VARIABILITY IN DAPHNIA 445 Immediately before the daily mensurations note was taken of cast carapaces and the number of young released. These were removed at the time of their discovery. Results and Discussion Longevity Some 82 animals were observed in these experiments. Figure 2 is a survival curve. Fifty-one animals lived for twenty instars and of these, 3 continued to the twenty-fifth instar. Bourguillaut de Ker- herve (1926) observed two Daphnia magna for nineteen instars. Each one released nineteen clutches of young a
. The Biological bulletin. Biology; Zoology; Marine biology. GROWTH AND VARIABILITY IN DAPHNIA 445 Immediately before the daily mensurations note was taken of cast carapaces and the number of young released. These were removed at the time of their discovery. Results and Discussion Longevity Some 82 animals were observed in these experiments. Figure 2 is a survival curve. Fifty-one animals lived for twenty instars and of these, 3 continued to the twenty-fifth instar. Bourguillaut de Ker- herve (1926) observed two Daphnia magna for nineteen instars. Each one released nineteen clutches of young and since not more than one clutch of young is released each instar and at least five instars precede the release of the first clutch of young, these two Daphnia magna lived. Fig. 1. Diagram showing method of making measurements. T, total length, longest dimension of animal exclusive of spine. C, carapace length, longest dimension of the carapace exclusive of spine. H, height, the shortest distance between two lines tangent to the carapace and parallel to the line of T. This measure of height is affected very little by the number of young in the brood chamber. for twenty-four instars or more. He cites 4 other individuals which must have reached the twenty-second, the thirteenth, the tenth, and the sixth instar, respectively. Anderson (1932) observed some 30 Daphnia magna for fourteen instars, 32 for thirteen instars, and others for a smaller number of instars, all from the time of release from the mothers. Rammner (1928) observed one Scapholeheris mucronata for seventeen instars and another for nine. Rammner (1929) cites others that have been observed for shorter times. Ingle, Wood, and Banta (1937) have observed individually reared Daphnia longispina for over twenty-five instars. Of the 82 animals observed in the present study, 71 were primiparous during the fifth instar and 9 during the sixth, while the remaining 2 died during the second and third instars. The number of. Pleas
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