. Chemical embryology. Embryology. 790 BIOPHYSICAL PHENOMENA [PT, III 5-3. The Osmotic Pressure of Aquatic Arthropod Eggs The osmotic behaviour of the amphibian egg is to some extent paralleled by that of the eggs of cladocerans, on which Przylecki has made notable studies. He found that the youngest embryos in his series had the lowest osmotic pressures; thus at 6 hours it was A — 0-245° for Simocephalus vetulus, and — 0-186° for Daphnia magna. As development pro- ceeded, the pressure steadily rose, reaching at 54 hours — 0-752° in the former case, and at 84 hours — 0-739° in the latter. The
. Chemical embryology. Embryology. 790 BIOPHYSICAL PHENOMENA [PT, III 5-3. The Osmotic Pressure of Aquatic Arthropod Eggs The osmotic behaviour of the amphibian egg is to some extent paralleled by that of the eggs of cladocerans, on which Przylecki has made notable studies. He found that the youngest embryos in his series had the lowest osmotic pressures; thus at 6 hours it was A — 0-245° for Simocephalus vetulus, and — 0-186° for Daphnia magna. As development pro- ceeded, the pressure steadily rose, reaching at 54 hours — 0-752° in the former case, and at 84 hours — 0-739° in the latter. The curve is shown in Fig. 183 taken from Przylecki's paper. The eggs were par- thenogenetically " fertilised," and the osmotic pressure was not determined by direct freez- ing-point measurements, but by observing how strong a v''glucose solution was required A(°). o Simocephalus vetulus • Daphnia pulex(embryo) X " " (perivitelline liq.) © Daphnia magna(parthenogenetic) B " " (ordinary fertilsation) + " " (perivitelline liq.) Fig. to make no change in ^gg- or embryo-volume^. Przylecki regarded the rise in osmotic pressure as largely due to the formation of osmotically active substances in metaboUsm. At the 6th hour the egg-membrane is in a state of tension, which augments until the 24th hour (120 per cent.), but then ceases altogether up to the 60th hour, after which it rises again (to 167 per cent.), as is shown in Fig. 184. In spite of the mounting osmotic pressure, then, there is a period during which no increase in membrane tension takes place'^. At this time the membrane does not return to its original state if the pressure is relieved by pricking the Qgg, but has evidently expanded in a more plastic manner. At the 60th hour the outer membrane (egg-membrane) bursts, and the larval membrane begins to expand. The growth of the embryo in volume follows these limiting factors. In a second paper, Przylecki confirmed the earlie
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