. Chemical embryology. Embryology. SECT. 5] IN ONTOGENESIS 811. â¢StrongylocentroUiS whole period ⡠⢠» between 4 c stage S^blastula(primitive mesenchyme) B â Strongyjocentrotus between blastula&, 3 spicule stage Strongylocentrotus &.Echinu8 p® â¢9 2-0 2-2 2-3 2-4 2-5 2'G 38 -40 '42 -44 -46 -48 -50 -52 '54 -56 '58 -60 -62 Rana ⢠in Fig. 195. In the case of the frog, the curve appears to drop only on one side. The zone within which normal segmentation would proceed also differed markedly for the two echinoderms; for in- stance, it was A â 0-63° in the case oiEchinus and only â0-57
. Chemical embryology. Embryology. SECT. 5] IN ONTOGENESIS 811. â¢StrongylocentroUiS whole period ⡠⢠» between 4 c stage S^blastula(primitive mesenchyme) B â Strongyjocentrotus between blastula&, 3 spicule stage Strongylocentrotus &.Echinu8 p® â¢9 2-0 2-2 2-3 2-4 2-5 2'G 38 -40 '42 -44 -46 -48 -50 -52 '54 -56 '58 -60 -62 Rana ⢠in Fig. 195. In the case of the frog, the curve appears to drop only on one side. The zone within which normal segmentation would proceed also differed markedly for the two echinoderms; for in- stance, it was A â 0-63° in the case oiEchinus and only â0-57° in the case of Strongylocentrotus, while in the case of Rana it was only â 0-17°. On the other hand, the zone between the os- motic pressures which caused death was relatively wider in the case of the amphibian than in the case of the two echinoderms. The effect of osmotic pressure on the embryos, moreover, was not the same at all stages. As regards mortality, the sensitivity of frog embryos to hypertonic solutions augmented with age; thus at the 8-cell .stage they were killed in 24 hours by solutions of A -^.0-95°, but at the time of hatching they we^ killed in 24 hours by a solution of only â 0-43°. On the other hand, the embryos of Strongylocentrotus lividus supported changes of osmotic pressure better the^older they were. As regards speed of development between given stages, this also was affected differently. As is seen from Fig. 195, between the 4-cell stage and the appearance of the first mesenchyme cells, the speed of development falls off distinctly less slowly from the optimum with change of osmotic pressure than it does between the appearance of the first mesenchyme cells and the three spicules of the pluteus. Faure-Fremiet made parallel experiments on the eggs of Sabellaria alveolata, and obtained precisely similar results. Fig. 196 taken from his paper shows the usual bell-shaped curves, resulting from the plot of active osmotic c
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Keywords: ., bookcentury1900, bookpublishernewyorkthem, booksubjectembryology
