588 Bashford Dean Memorial Volume 



Dean's drawing (Text-figure 25) is raade from a section cut parallel to the long axis 

 of the future embryo. I wish to call attention particularly to the slight difference in the 

 portrayal of the thicker margin by Dean and by Nishikawa. Dean represents the limit of 

 the thickened end by a smoothly curved unbroken nearly vertical line separating the 

 blastomeres from the region of pericytes. Nishikawa, whose drawing was made with 

 a higher magnification, shows one of the embryonic cells incompletely cut off from the 

 yolk mass (Text-figure 23). If this cell had gone on to complete separation, then 

 the margins of the two figures would have been almost identical. 



GASTRULAE 



Earliest of all, Nishikawa collected but failed to figure and describe a gastrula of the 

 frilled shark. Of his one egg he states — "I have also obtained a gastrula, which was oval 

 in form and 3 mm. in length. I have nothing special to add about it as it was like the 

 gastrula of any other shark". But was it? There is so much variability about Chlamydo- 



Text-figure 26 

 Sketches from Dean's notebook. A and B — /^"!;^=^ ,^— ^^ 



"Gastrulae 2 stages;" C one of "3 oblong eggs." f C ^J\ /Q[j^ 

 For "2 drawn" — no gastrulae shown — see Fig- V y' 'v^ / 



ures 2 and 3, plate I. C was never "drawn," b 



though labelled "probably gastrula." 

 Sketches by Bashford Dean. 



selachus that one wishes for surface views and sections. To me this seemed very small for 

 a gastrula and at first I was inclined to think that Nishikawa was in error, that no shark 

 gastrula could be so small as 3 mm. in greatest diameter. But on looking up the literature 

 I found that Ziegler (1902, p. 117) figures a gastrula of Torpedo 2 mm. long. And Scammon 

 (1911) portrays gastrulae of Squalus acanthias 4.2 and 4.4 mm. long. Thus both Ziegler 

 and Scammon give presumptive evidence that Nishikawa was correct. 



On the page of Dean's notebook headed "Material and List of Figures", one finds this 

 notation, "Gastrulae 2 stages", followed by two pencil sketches showing eggs with 

 relatively large circles on them like those in Figures 4, 5, and 6, plate I. I have thought it 

 well to reproduce these pencil sketches as Text-figure 26. Then on the page of the note- 

 book on which Dean described the "3 oblong eggs", referred to later, there is a pencil 

 sketch of an oblong egg with an incomplete ring placed asymmetrically (Text-figure 26), 

 and having at the opposite end a tendril-bearing process. This egg is labelled "stage 

 early, probably gastrula". Two of these "oblong eggs" were drawn and are identified 

 and reproduced as Figures 2 and 3, plate I. Of the oblong egg with the gastrula, un- 

 fortunately no finished drawing was ever made. 



On still another page of the notebook referred to is the heading, "Earlier stages, 3 

 eggs C B. & A." Then follows brief descriptions of two which he thought were blastulae 

 and of a third which he believed to be a gastrula. Here follow his descriptions: 



