. Chemical embryology. Embryology. SECT. 6] OF THE EMBRYO 847 selective absorption of the carbon dioxide produced by the organism as a whole by the mesenchyme cells for the manufacture of calcium carbonate, a process which might well be expected to make the liquid of the blastocoele cavity more alkahne than usual. Next Bouxin found that a fall of pH irrespective of the acid employed would produce in Strongylocentrotus lividus larvae a retardation of skeleton formation or a complete stoppage, or even if the p¥L was lowered below 6-4 a re- gression of spicules already formed. Rapkine & Bouxi


. Chemical embryology. Embryology. SECT. 6] OF THE EMBRYO 847 selective absorption of the carbon dioxide produced by the organism as a whole by the mesenchyme cells for the manufacture of calcium carbonate, a process which might well be expected to make the liquid of the blastocoele cavity more alkahne than usual. Next Bouxin found that a fall of pH irrespective of the acid employed would produce in Strongylocentrotus lividus larvae a retardation of skeleton formation or a complete stoppage, or even if the p¥L was lowered below 6-4 a re- gression of spicules already formed. Rapkine & Bouxin accordingly micro-injected indicators into the blastocoele cavity at different ex- ternal hydrogen ion concentrations, and in fact found that when the exterior /?H went down to 6 that of the blastocoele cavity also went down, and almost as far, keeping above it, however, to the extent of two or three tenths of ^^h a />H unit. In the extreme cases there seemed, then, to be an actual solution of the spicule. Rapkine & Bouxin found that during this process the j&H of the liquid in the blastocoele cavity was maintained rather stable at ^^' ^° " />H 6*25, and they suggested that the regression of the skeleton might to a certain extent be considered as a defence mechanism in view of the fact that death invariably occurred when the blastocoele pYi had reached 6-o. In the case of younger embryos, where the mesenchyme cells had just appeared, a small fall in external/>H causes a retardation or an inhibition of skeleton formation, while the j&H remains at about 7-4; thus the mesenchyme cells are removing carbon dioxide, but the external acidity prevents the j&H rising. Contributory evidence showing the retention of carbon dioxide during spicule formation was provided by Vies & Gex, who placed developing echinoderm eggs in a small chamber surrounded by a dilute indicator, and then examined the system from time to time spectrophotometrically. They obta


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Keywords: ., bookcentury1900, bookpublishernewyorkthem, booksubjectembryology