. Chemical embryology. Embryology. 370 ON INCREASE IN SIZE [PT, m Amphibia. Frog. In the case of amphibia, where the cleavage in the egg is more or less inclusive of the yolk-laden portion, it is not possible to obtain data for the weight of the embryo itself, for, before hatching, although the protoplasm is constantly increasing at the expense of the yolk, the two elements cannot be separated, and therefore cannot be weighed in isolation. This appears in the figures of Faure- Fremiet & Dragoiu; Schaper; Davenport; and Bialascewicz, and must always be taken into account when differences be
. Chemical embryology. Embryology. 370 ON INCREASE IN SIZE [PT, m Amphibia. Frog. In the case of amphibia, where the cleavage in the egg is more or less inclusive of the yolk-laden portion, it is not possible to obtain data for the weight of the embryo itself, for, before hatching, although the protoplasm is constantly increasing at the expense of the yolk, the two elements cannot be separated, and therefore cannot be weighed in isolation. This appears in the figures of Faure- Fremiet & Dragoiu; Schaper; Davenport; and Bialascewicz, and must always be taken into account when differences between species in water-content and other constants are under consideration, for much confusion may be caused by not distinguishing carefully between yolk plus embryo and embryo alone. Reptilia. Snake. Bohr's very few figures on Coluber natrix are all that are avail- able. (Appendix i. Table 2.) Birds. Chick. It is on this animal, as might be expected, that the greater part of the work on embryo- nic growth has been done. Hasselbalch, in the course of his work on the respiration of the chick embryo, ob- tained a regular series for a race not given. These corre- sponded well enough with the earlier data of Falck (also from an unknown breed), which were the first to be published, appearing in 1857. Hasselbalch's curve is shown in Fig. 21, in which for the first time we see the usual '' embryo-placenta relation'' in the form of a weight of extra-embryonic structures larger than the embryo in the earliest stages, but soon falling below it.^ relation between the two as follows: 4-0 2'0 1«0 O Membranes • Embryo. Hasselbalch calculated the See also Fig. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Needham, Joseph, 1900-. New York: The MacMillan Co.
Size: 1372px × 1821px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookpublishernewyorkthem, booksubjectembryology
