The Embryology of Chlamydoselachus 619 



proximal portions of both vitelline artery and vein. The artery extends out from under 

 the head of the embryo as a single vessel until it forks narrowly into two branches before 

 passing over the equator of the egg. The dendritic system of vessels under the tail of the 

 embryo is venous and laden with food absorbed from the yolk mass. This circulation on 

 the upper side of the egg carrying the 39'mm. embryo is essentially like that portrayed 

 on a flat surface by Balfour (Text'figure 30). Unfortunately there is no drawing showing 

 the relation of arterial and venous vessels on the opposite side of the egg of this 39'mm. 

 Chlamydoselachus. For this we shall have presently to go to the drawings of the 43' 

 mm. embryo and its yolk sac. 



Arterial and Venous Trunks in the Yolk Cord. — Inspection of the yolk cord of the 

 39'mm. embryo (Figure 51, plate V) shows that the artist has not differentiated 

 the trunks of artery and vein in the cord. They are not portrayed in the 43'mm. 

 specimen (Figure 7, plate I). In the 50'mm. embryo the arterial and venous vessels are 

 plainly shown in the yolk stalk (Figure 9, plate I), but (as in the 39'mm. specimen) they 

 are not distinguished from each other. Probably they run side by side and are too small to 

 be shown separately in these drawings made in this small but natural si2;e. In the 175' 

 mm. fishlet (Figure 11, plate I) the yolk cord cannot be seen due to the position of the 

 wide head. Probably it is too short for the yolk'cord trunks to be seen, as is the case in 

 the 390'mm. shark (Figure 49, plate V). 



Yolk-Sac Circulation of the 43'mm. Specimen 



This is the only embryo and egg of Chlamydoselachus whose vitelline circulation has 

 previously been described. This was done by Nishikawa (1898, p. 97) who had at least 

 six eggs with young embryos (32-60 mm. long) but he seems not to have been aware of the 

 studies of his predecessors — not even of Balfour's well'known work. Had he consulted 

 this author, he surely would not have made such errors as fill his page and give point to 

 Balfour's remark (1885, p. 465) "The observations recorded on the subject [the circulation 

 of the yolk'sac in sharks] are, so far as I am acquainted with them, very imperfect, and in 

 most cases the arteries and veins appear to have been transposed". What our Japanese 

 author wrote illustrates this point. 



The circulation in the yolk'sac could be clearly traced and is reproduced in Figs. 1 and 2 

 [my Text-figure 4, and Figures 7 and 8, plate I]. On leaving the umbilical cord [yolk cord] 

 the artery and vein run in opposite directions. The former receives on its course a number of 

 smaller veins from the two poles of the yolk-sac, and divides finally into three main branches. 

 The artery runs for some distance without giving off any branch, and then divides into two 

 main vessels, which, after running for a short distance parallel to each other, form at last, on 

 the opposite side of the yolk-sac, an elongated, irregularly shaped arterial ring, from which 

 numerous small vessels radiate toward the periphery. The arterial ring just mentioned is still 

 wide apart in the embryo of 32 mm., but in one of 43 mm. its two halves almost touch each 

 other [Figure 8, plate I j, but in other respects there is no change in the circulation. 



Nishikawa's description contains many errors. An attempt was made by the 

 present writer to correct these by insertions in brackets, but when done the resulting 

 paragraph was so conglomerate and confusing that it was discarded. It has seemed best 

 to quote just what Nishikawa wrote, and then to describe in my own words the cir' 



