590 Bashford Dean Memorial Volume 



But suppose that the artist had before him living eggs, would not the whole germinal 

 area have the same color? The answer to this question is I believe to be found in my 

 observations of living gastrula stages in the large thick-shelled intra-oviducal eggs of the 

 nurse shark, Ginglymo stoma cirratum. On some eggs examined on July 21, 1912, I found 

 an orange'colored ring enclosing an area which covered one-fourth to one-third of the 

 upper (or visible) side of the egg. This object was more plainly seen by cutting a window 

 in the capsule over this colored ring and removing some of the glairy liquid surrounding 

 the egg. Then, when a little sublimate-acetic was dropped on it, the whole blastoderm 

 became visible with the beginning embryo in it. This was again seen on July 22, on an 

 egg from another female. From another egg I got a "Blastoderm about the size of a silver 

 dollar", and on another egg "Large blastoderm partly on top and partly on side of yolk". 

 Another had "Blastoderm covering a little more than half the upper side of yolk, with one 

 edge dipping over the side". On an egg examined on July 23, the "edge of the blastoderm 

 was a rusty orange; embryo transparent and colorless, only visible when in motion". In 

 the plates of the next article of this volume — that on the embryology of Heterodontus — 

 will be seen the same orange-colored ring of a blastodisc embracing an area covering one- 

 fourth to the whole of the upper visible surface of the 55-mm. egg with an embryo so 

 small and transparent as to be almost invisible. 



Thus the early gastrula stages of eggs of Chlamydoselachus, eggs alive or dead, were 

 presumably seen as drawn in Figures 4, 5, and 6, plate I. It drawn alive at Misaki then the 

 artist saw and drew the colored edges of the late blastodiscs. If the eggs had been "fixed", 

 then it must be concluded that they were in early gastrula stages before embryos had been 

 formed, but that as Balfour puts it "The embryonic rim is represented by a darker shading 

 at the edge". Lastly it should be noted that these blastoderms in the gastrula (?) stages 

 shown in the figure cited cover a substantial part of the upper surface of the eggs. 



Finally, it must be said that if the eggs shown in Text-figure 26 are in the gastrula 

 stage as Dean expressly states, then the three eggs portrayed in greater size and detail in 

 Figures 4, 5, and 6, plate I, are also presumably in the gastrula stage. To me the sketches 

 all show eggs in the same stage. Nothing in drawings or text diiferentiates them. 



As noted at the beginning of this section, Nishikawa (1898) states that he obtained 

 an early gastrula. This was sectioned and the sections were in 1901 or 1902 turned over 

 to Dean. Among Dean's sHdes in my possession are five of serial sections of an early 

 gastrula of Chlamydoselachus. I presume that these were sections prepared by Nishikawa 

 and presented to Dean. In Dean's notebook are outline sketches made from these sections. 

 The plane of the sections is oblique to the axis of the forming embryo and consequently 

 these sections are not very favorable for study. In general the mode of development is 

 like that found in other elasmobranchs. 



LATER DEVELOPMENT 



In this study of the frilled shark, my readers and I have now come to that part which 

 perhaps holds the most interest since it is the most concrete — the study of the embry- 



