. The biology of the frog. Frogs. 94 THE BIOLOGY OF THE FROG smaller as the process of in-pushing is completed. The pro- cess of gastrulation, which is exemplified in its typical form in the development of a starfish or sea-urchin, becomes very much modified in different animals. Such is the case in the development of the frog. The large accumulation of yolk at the vegetal side of the blastula prevents the invagination of this region from taking place in the typical way. The same. Fig. 19. — SagittaJ section through a frog embryo. 5, blastocoel or segmen- tation cavity; DP, lip of blastopore;
. The biology of the frog. Frogs. 94 THE BIOLOGY OF THE FROG smaller as the process of in-pushing is completed. The pro- cess of gastrulation, which is exemplified in its typical form in the development of a starfish or sea-urchin, becomes very much modified in different animals. Such is the case in the development of the frog. The large accumulation of yolk at the vegetal side of the blastula prevents the invagination of this region from taking place in the typical way. The same. Fig. 19. — SagittaJ section through a frog embryo. 5, blastocoel or segmen- tation cavity; DP, lip of blastopore; EE, outer or epidermic layer of ectoderm; EN, inner or nervous layer of ectoderm; Y, yolk cells. (After Marshall.) end is reached partly by a process of in-pushing and partly by the overgrowth of the white pole by the dark. The in- pushing and overgrowth take place more on one side of the egg than the other, and these processes are first indicated by the appearance of a crescentic groove a little below the equator of the egg. The crescent represents the beginning of the blastopore. The groove is deepest at the center and. 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 Holmes, Samuel J. (Samuel Jackson), 1868-1964. New York Macmillan
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectfrogs, bookyear1916
