. The Bashford Dean memorial volume :. Fishes; Sharks; Fishes, Fossil. The Embryology of Heterodontus japonicus 737 Text-figure 55. Transverse section through the posterior portion of a blastoderm of Heterodontus phiHipt in a stage somewhat later than the preceding, but before the differentiation of the notochord. ect, ectoderm; end, entoderm; ent, archenteric After Haswell, 1898, Fig. 8, pi. V. cavity. end &CL. In Heterodontus phillipi, as in other Elasmobranchs, gastrulation takes place mainly by a process of involution. According to Haswell (1898) the first phase of gastrulation consist
. The Bashford Dean memorial volume :. Fishes; Sharks; Fishes, Fossil. The Embryology of Heterodontus japonicus 737 Text-figure 55. Transverse section through the posterior portion of a blastoderm of Heterodontus phiHipt in a stage somewhat later than the preceding, but before the differentiation of the notochord. ect, ectoderm; end, entoderm; ent, archenteric After Haswell, 1898, Fig. 8, pi. V. cavity. end &CL. In Heterodontus phillipi, as in other Elasmobranchs, gastrulation takes place mainly by a process of involution. According to Haswell (1898) the first phase of gastrulation consists of an arching upward of the posterior portion of the blastoderm, so that where it passes into the parablast it becomes, for a short distance, vertical. It soon inclines forward (as illustrated in my Text'figure 53), forming the embryonic rim which extends along the entire posterior margin of the blastoderm. At the same time the accumulation of cells at the posterior end increases at the expense of the segmentation cavity. In the stage represented by Text'figure 53 the segmentation cavity has become extremely shallow, and its roof has acquired a compact epithelial character. The stage represented by Text'figure 54 possesses a definite entoderm, hence it is a well'established gastrula. To the present writer it seems that the cleft, separating the poorly'defined layer of cells marked end' from the irregular layer above, is mainly an artifact. Text'figure 55 is a transverse section through the archenteric cavity of a stage a little farther advanced than the one shown in Text'figure 54. It shows no new features, but is helpful in afibrding a different point of view. At first the floor of the archenteric cavity consists only of yolk; but soon the anterior portion of the archenteron will form an entodermal pocket, the fore' Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of th
Size: 2593px × 964px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., book, bookcentury1900, booksubjectfishes, booksubjectfishesfossil
