586 Bashford Dean Memorial Volume 



Nishikawa (I898j states that the yolk has a pinkish color. Presumably his obser- 

 vations were made on fresh material. In our specimens, in various stages of development 

 but not including blastula and gastrula stages, the yolk is usually pale yellov;? but occasion' 

 ally some portions are very pale pink. That Dean had Hve eggs with pink yolk is evi- 

 denced by his two drawings in color — Figures 49 and 50, plate V. 



Among Dean's few Chlaynydoselachus slides there are none of either whole mounts or 

 sections of the blastula stage. However, there is evidence that, along with the other 

 materials turned over to him by Nishikawa, there were sections of segmenting blasto- 

 derms . In one paragraph of his notebook are a number of rough outline sketches of sections 

 of blastulae labelled "Nishikawa's Slides Early''. Nishikawa (1898, p. 97) portrayed 

 {Text-figure 23) without caption one edge of a segmenting blastoderm but never carried 

 his studies further. Dean had these slides and drew a number of the sections. 



Among Dean's finished drawings are two, labelled Chlaynydoselachus, which show 

 sections through an early cleavage stage and a late blastula stage respectively. These are 

 reproduced as Text-figures 24 and 25. The magnifications are not given, and the slides 

 from which the drawings were made have been lost. There is nothing very striking 

 about the mode of development portrayed, since it is typically elasmobranch; but Dean 

 in his only pubhcation f 1903 ) dealing with the development of Chlamydoselachus — a brief 

 note — calls attention to "the great depth of the zone of yolk nuclei". This is well shown 







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Text-figure 24 

 A section through the germinal area of a segmenting egg of ChlamvcJoseldchus in an early blastula 



stage, showing the blastoderm (at left, above) and the broad and deep zone of periblast. At the 

 left, about four-fifths of the lateral extent of the periblast has been trimmed off from the original 



drawing; at the right, one-fourth. 

 Drawing by Bashford Dean. 



