The Embryology of Chlamydoselachus 603 



and slender yolk stalk allows the embryo considerable freedom of motion. Embryo and 

 egg are undoubtedly drawn in natural si2,e. No mention of this figure is to be found in 

 Dean's notebook. 



Proceding out from under the head of the embryo is the single vitelline artery, which, 

 after traversing about 90° of the circumference of the yolk sac, divides into two. Coming 

 in under the tail of the embryo is the vitelline vein which receives at right angles many 

 tributaries. These are abundant in the proximal portion of the vein even to the point 

 where it enters the yolk stalk. The complete circulatory pattern will be considered 

 later when older stages are described. Note should be made of the pale pink color of the 

 surface of the yolk mass. This drawing confirms Nishikawa's statement that "The yolk is 

 of a pinkish color". 



Nishikawa's 43'mm. Embryo on its Yolk-sac. 



There is no specimen of this size called for in Dean's list, but such an embryo is shown 

 in his Figure 7, plate I. Here is the history of this egg as I have reconstructed it. 



The egg with the 43'mm. embryo on it which Nishikawa figured in an outline pen 

 and ink drawing (my Text'figure 4) was redrawn for Dean in pencil for lithographic 

 reproduction, as may be seen by comparing the outline text'figure with Figure 7, plate I. 

 This, I conjecture, was done not so much to fill in a gap in the series (there are no large 

 drawings showing details of the morphology of this embryo) as to show the egg capsule 

 and the yolk'sac circulation. Here it may merely be noted that the large unbranched 

 vessel on the yolk is an artery, the much'branched one a vein. This specimen has already 

 been studied for the structure of the capsule in the section on "The En capsuled Egg". 

 The yolk-sac circulation will be described later. Both original figures- -text and plate — 

 show egg and embryo in natural size. Even in figure 4 (reproduced natural size), the little 

 fish is too small to show any details. 



Dean's Embryo of 46 Millimeters 



The "List" does not call for a specimen or figures of an embryo of this size, but I find 

 carefully executed drawings in dorsal, ventral and lateral views. Moreover, two of 

 these drawings are labelled in Dean's writing. Grouped with the three drawings, of the 

 46'mm. embryo are three each for embryos of 54, 66, and 103 mm. These drawings, all 

 done in one technique by the same hand and mounted on a different kind of board, look to 

 me to have been made more recently than any drawings thus far studied and more recently 

 than single drawings of larger and older specimens to be studied later. All the older 

 drawings of embryos both smaller and larger than these four are mounted on a poor 

 quality of yellow cardboard, old, dog-eared, soft and crumbling. The drawings themselves 

 are yellow with age and often spotted and dirty. These drawings are years older than the 

 four sets referred to. The most tangible evidence of the technique of the newer drawings 

 is found in the "window" in the eyes of the figures of these four sets of embryos. There is 

 no evidence as to where and when they were made. 



Dorsal Aspect. — The original drawing of this 46'mm. embryo seen from above 

 measures 257 mm. (i.e, x 5.6). It is reproduced in Figure 28, plate III. When this drawing 



