. The development of the frog's egg; an introduction to experimental embryology. Embryology. 1-iO DEVELOPMENT OF THE FROG'S EGG [Cii. XIII The main differences that exist between the methods of forma- tion of neurenteric canal and anus in the frog and in urodeles are these: In the frog the ventral lip of the blastopore grows forward during the closure of the blastopore, and only subse- quently a new opening forms at the point from which the for-. FiG. 38. —Embryo of Kaua temporaria at time of hatching. ward growth began (Fig. 37, A, B). In the urodeles (newt and Amblystoma) the ventral lip of
. The development of the frog's egg; an introduction to experimental embryology. Embryology. 1-iO DEVELOPMENT OF THE FROG'S EGG [Cii. XIII The main differences that exist between the methods of forma- tion of neurenteric canal and anus in the frog and in urodeles are these: In the frog the ventral lip of the blastopore grows forward during the closure of the blastopore, and only subse- quently a new opening forms at the point from which the for-. FiG. 38. —Embryo of Kaua temporaria at time of hatching. ward growth began (Fig. 37, A, B). In the urodeles (newt and Amblystoma) the ventral lip of the blastopore remains stationary, it retains its first position, and the anus forms directly from its posterior end. The Digestive Tract and the Gill-slits The origin of the archenteron has been described in Chapter VI. At the time when the yolk-plug is drawn in from the surface, the archenteron has begun to enlarge (Fig. 26, A). A series of cross-sections (Fig. 26, B-E) of an embryo at this stage show that the dorsal and lateral walls of the archenteron consist of a single layer of endodermal cells, wliile the floor of the archenteron is formed by the upper surface of the yolk- mass. The uppermost cells of the yolk-mass show, to some extent, a tendency to arrange themselves in a single layer bounding the archenteron. Shortly after this period the embryo increases in length, and the archenteron is correspondingly drawn out (Fig. 37). The anterior end of the archenteron enlarges, and the yolk-mass is pushed posteriorly. As a result the middle and posterior parts of the archenteric cavity become smaller than they were in the earlier stages (Figs. 39, 40). The walls of the anterior portion of the archenteron are thin, and composed of a single layer of cells. A blind diverticulum extending from this enlarged. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustr
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectembryology, bookyear1
