The Embryology of Chlamydoselachus 



609 



the 54'mm. in Figure 34, plate III. The head of the former looks decidedly older than 

 that of the latter. The head in front of the mouth is shorter, and across the mouth 

 region it is narrower. The nasal cavities are located well forward. The mouth of the 

 55'mm. fish looks less embryonic, older and better developed. The gill-arches are not so 

 dilated and the filaments are, as noted above, entirely lacking. In both, the first gill'flap 

 is continuous across the isthmus. The sensory-canal system on the under side of the 

 head is well developed. 



Here are two embryos differing in length by but one millimeter, but varying widely 

 from each other. The morphological differences are principally in the head and mostly in 

 the ventral head. In degree of development the mouth structures so differ that, on the 

 basis of this one character with no others visible, one would separate these embryos as of 

 two widely different stages. Whether this represents an actual difference in embryos 

 of a shark whose variableness is greater than in any other known to me, or is due to a 

 difference in artists cannot be said. Were the two embryos at hand, the matter might 

 possibly be settled. 



Carman's Embryo of 64 Millimeters 



When Dr. Thomas Barbour, now Director of the Museum of Comparative Zoology, 

 Cambridge, Mass., returned in 1906 from a visit to Japan, he brought with him this 

 embryo. It was figured but not described by Samuel Carman in 1913 (Figs. 7 and 8, 

 pi. 61). For its historical interest and for the sake of completeness, Carman's figures 

 (lateral and ventral aspects) are reproduced herein as text'figures and are described. 



Lateral Aspect. — Comparison must be made of the 64'mm. embryo (Text'figure 

 29a) with that of 55 mm. (Figure 36, plate III). Excepting in the head region, the two 



Text-figure 29 

 Two views (lateral and ventral) of a 64-mni. embryo of Chlamydoselachus. 

 After Carman, 1913, Figs. 7 and 8, pi. 61. 



