The Embryology of Chlamydoselachus 605 



Head of a 48-mm. Specimen in Ventral View 



We now return to Dean's ''List'\ which calls for "Embr. of 48 mm. ventral (head)" 

 and on the opposite page is "48? Another, head only stained". Among the older draw- 

 ings I find one without the figures "48" but with the significant label "head only stained". 

 Moreover the drawing (Figure 31, plate III) shows this head in ventral view. From these 

 data, and despite the fact that this "head . . . stained" in ventral view looks somewhat 

 younger than the head of the 46'mm. embryo in ventral aspect and decidedly younger 

 than that of the 54'mm. specimen (Figure 34, plate III), I believe that this head shown in 

 ventral view is that of the 48'mm. embryo. Nishikawa had a 49'mm. specimen, and I 

 believe that the "head only, stained" shown in Figure 31, plate III, is Nishikawa's speci' 

 men stained in toto (as was the practice in those days) but never sectioned. 



Compared with the 46'mm. embryo (Figure 30, plate III), the head looks wider and 

 more rounded, the eyes less prominent and the nasal organs better developed. The mouth 

 is less advanced than that of the 46'mm. specimen. The upper jaw still has a definite 

 median gap between the two halves, but the lower seems to be about normal for this 

 stage. The gill'flaps are widely spread, especially the first pair — which are not continu- 

 ous across the isthmus. Filaments seem to be absent, save in the first and second gill'slits 

 on the right side. The pectoral fins are hardly so well developed as those in the 46'mm. 

 embryo. The gular fold is lacking. That the 48'mm. embryo seems younger than the 

 46'mm. specimen is probably an individual variation. 



Nishikawa's 50-mm. Embryo on its Yolk Sac 



Nishikawa (1898) had a 50'mm. embryo of Chlamydoselachus on its yolk sac. He 

 did not have either yolk sac or embryo drawn, but he does portray the head only in both 

 dorsal and ventral aspects (Text'figure 28a and b). Whether Dean got a specimen of 

 this siz;e, through the help of Kuma or the commercial fishermen, cannot be said. But 

 I suspect that Dean's drawings of egg and embryo (Figures 9 and 10, plate I) were made 

 from Nishikawa's specimen. I have shown that Dean's Figures 7 and 8, plate I, are 

 duplicates of Nishikawa's Figs. 1 and 2 of his pi. I. Here compare my Text'figure 4 with 

 Figure 7, plate I. Now the capsules of the egg seen in Figures 7 and 9 plate I, are of the 

 same type. Dean may have had eggs with capsules such as these, but, since no others of 

 this kind are figured by him, I doubt it. In my judgment, the egg with the 50'mm embryo 

 is the one listed by Nishikawa, and, since it had not been drawn for Nishikawa's article 

 (1898), it was turned over with other specimens for Dean's studies. 



On its Yolk Sac. — This 50'mm. embryo (shown in half size in Figure 9, plate I) is 

 of course too small (even in Dean's drawing in natural size) to show any morphological 

 details. It was probably drawn to show the capsule and the circulation over the yolk sac. 

 The capsule has already been studied. It is a counterpart of that around the 43'mm. 

 embryo and its yolk sac. The yolk circulation is somewhat more advanced than that on 

 the yolk of the younger specimen. It will be discussed shortly. Fortunately the details 

 lacking in Figure 9, plate I, may be found in Nishikawa's line drawings of the head (his 

 Figs. 7 and 8, plate IV) which will now be considered. 



