. The Bashford Dean memorial volume :. Fishes; Sharks; Fishes, Fossil. Text-figure 46. Some stages of mitosis in the blastomeres of Heterodontus japonicus: A, metaphase or middle phase of mitosis; B, anaphase; C, early telophase. In C, the chromosomes have begun their transfor- mation within chromosomal vesicles. From drawings left by Bashford Dean. derm is surrounded by a very shallow circular groove. The type of cleavage is, of course, discoidal. It is sufficient to add that the cleavage patterns of these blastoderms are not essentially unlike those of other Elasmobranchs: e. g., Scyllium as
. The Bashford Dean memorial volume :. Fishes; Sharks; Fishes, Fossil. Text-figure 46. Some stages of mitosis in the blastomeres of Heterodontus japonicus: A, metaphase or middle phase of mitosis; B, anaphase; C, early telophase. In C, the chromosomes have begun their transfor- mation within chromosomal vesicles. From drawings left by Bashford Dean. derm is surrounded by a very shallow circular groove. The type of cleavage is, of course, discoidal. It is sufficient to add that the cleavage patterns of these blastoderms are not essentially unlike those of other Elasmobranchs: e. g., Scyllium as portrayed by Riickert, 1899, Figs. 10 and 11, pi. LII. There is a noticeable gap between the figures thus far discussed and the one il' lustrating the earliest gastrula stage. This gap is partly bridged by Dean's drawing show- ing the segmentation cavity of a blastoderm dissected off the yolk mass and viewed by transmitted light. Upon focussing with the low power of the microscope through the thin roof of the blastocoele, an optical section is obtained which shows that the cavity is crescent-shaped (Figure 10, plate I). There are no other figures, suitable for reproduction, showing the cellular structure of the blastoderm in a later stage of cleavage; but the colored drawing reproduced as my Figure 80, plate VII, shows the general appearance of what is presumably a late blastula (compare Figure 44, plate IV). In Figure 80, plate VII, the blastoderm is probably con- fined to the elliptical reddish area; but when the corresponding figure on plate IV is Text-figure 47- Late stages of mitosis in the blas- toderm of Heterodontus japonicus. In A, late telophase, the forma- tion of chromosomal vesicles is nearly complete; in B, the chro- mosomal vesicles of a single daughter nucleus are represented. From drawings left by Bashford Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearanc
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