The Embryology of Heterodontus japonicus 



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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 Dean. 



