. Chemical embryology. Embryology. SECT. 6] OF THE EMBRYO 907 yoLk-sac period-*« hunger— provisionally it may be accepted. Fig. 239 gives a graph plotted from their data. The percentage growth-rate falls markedly at the end of the first period, only to rise again to a maximum during the free- swimming period. Everything, in fact, points to a resumption of the growth-process as soon as an unlimited supply of water is avail- able, which will only fall off again when the nutriment in the yolk-sac is beginning to be exhausted. Kronfeld & Scheminzki pointed out that the decline in the growth-ra
. Chemical embryology. Embryology. SECT. 6] OF THE EMBRYO 907 yoLk-sac period-*« hunger— provisionally it may be accepted. Fig. 239 gives a graph plotted from their data. The percentage growth-rate falls markedly at the end of the first period, only to rise again to a maximum during the free- swimming period. Everything, in fact, points to a resumption of the growth-process as soon as an unlimited supply of water is avail- able, which will only fall off again when the nutriment in the yolk-sac is beginning to be exhausted. Kronfeld & Scheminzki pointed out that the decline in the growth-rate before hatching occurred before all the water in the yolk was finished, as would be expected in view of the osmotic pressure of the latter. They drew attention to ^ Schaper's well-known experi- 5 ment on frog embryos and J larvae, in which he placed them J in salt solutions, and, by thus I holding back the water which | they needed to absorb to form | their tissues, succeeded in in- ^ hibiting their growth. Kronfeld % & Scheminzki confirmed this ^ for the trout in some preliminary experiments. The question of whether growth of the trout fry can continue after the yolk has been used up was left open by Kronfeld & Scheminzki, but Weiss had previously maintained that this could occur, and Podhradski & Kosto- marov confirmed Weiss' results on carp alevins at the end of their yolk-sac period. It must be supposed that this growth is either due to the persistence of small amounts of yolk which gradually get used up after the yolk-sac has apparently disappeared, or to the utilisation of muscles or other tissue as nourishment instead of yolk. The latter process is suggested by the work of Krzinecki & Petrov^. The process of water-absorption by the amphibian larva during its development was studied also by Bialascewicz, who used the un- satisfactory but relatively easy method of measuring volume changes. In all his curves, a temporary reduction of volume is seen abo
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Keywords: ., bookcentury1900, bookpublishernewyorkthem, booksubjectembryology
