y 



The Embryology of Chlamydoselachus 6l7 



jaw. The nasal aperture of the embryo is not yet completely divided into two. The 

 gill'covers have pocket'like folds where they join the body. The first plainly extends 

 across the throat — i.e., the isthmus and throat are "cloaked". Note that there are visible 

 very short gill'fiilaments. The body is humped above and on the ventral edge is seen one 

 side of the tropeic folds. ^ Plainly visible is the latercsensory canal on the first gill'cover 

 and the lower jaw, and the lateral line extending along the body and the tail to its very 

 tip — with the previously noted irregularities under the dorsal fin. 



In this drawing, the artist has again inserted short dotted lines (in white) extending 

 dorsally from the lateral line. These are more widely spaced than the zigzag intersegment- 

 al grooves seen along the sides of the body. Examination of the original specimen and of 

 one but slightly smaller discloses that the intersegmental grooves above the lateral line are 

 occasionally visible. Nothing in this region in this fish could easily be mistaken for branch- 

 es of the lateral line. 



The fins are very like those of the adult, including the well-formed caudal fin with 

 the notch at the tip of the lower lobe — faintly presaged in the 103-mm. fish, but here seen 

 plainly for the first time in this drawing of a large frilled shark embryo. What more can 

 be said in description of this striking figure? The reader must study it for himself. 



THE YOLK-SAC CIRCULATION 



The vitelline blood vessels from small beginnings come finally to spread over all 

 the large yolk sac of Chlamydoselachus. Their function is to bring food stuff to the de- 

 veloping embryo. These vessels have been briefly referred to earHer in this paper in 

 describing certain embryos figured on their yolk sacs — the 39-mm. embryo (in color), the 

 43- and 50-mm. embryos and the l75-mm. fishlet (in gray), and lastly the 390-mm. shark 

 (in color). . The early stages of the development of this circulation are lacking in these 

 drawings but the intermediate and later stages are shown. These portrayals are so in- 

 formative as to call for special study. 



Opportunities to study the yolk-sac circulation on the eggs of sharks occur very 

 infrequently. In my investigations on live eggs and embryos of the sharks and rays else- 

 where referred to, I was so occupied with other observations that those on the yolk-sac 

 circulation were very incomplete. Dean's figures unfortunately do not show the early 

 stages, so to make things clear, I refer the reader to Balfour's classical work (1885, pp. 

 465-466, pi. 9). In this he figures (diagrammatically) and describes the early circulation 

 on the egg of Pristiurus essentially as it will presently be portrayed for Chlamydoselachus. 

 Here is a synopsis of what he wrote. 



As may be seen in Text-figure 30a, the blastoderm in this early stage covers about 

 three-fifths of the yolk. The embryo is found in the bay of the blastoderm and from under 

 its head extends forward the vitelline artery (a). This presently divides into two forks 

 right and left and these are the beginnings of the arterial ring. In Text-figure 30b, it is 



'For data concerning this extraordinary structure, found in no other shark, the reader must turn to Gudger and Smith (1933, 

 Article V of this Memorial Volume, pp. 283-284, Text-figure 1 2) by whom it is figured and comprehensively described. ; 



