The Embryology of Chlamydoselachus 539 



Dean portrays three eggs in blastula or gastrula stages in Figures 4, 5, and 6, plate I. 

 The yolks measure : A, 97 x 88 mm. ; B, 96 x 87; C, 90 x 87- Of eggs and early embryos in 

 stages of development comparable to Nishikawa's 43'mm. embryo, Dean had three drawn. 

 Figure 7, plate I shows a yolk 100 x 65 mm. with an embryo of 43 mm.; (as will be seen 

 later, this is a copy of Nishikawa's Fig. 1, plate IV); in Figure 9, plate I, the yolk measures 

 108 X 68, the embryo 50 mm.; and lastly there is the drawing in color, Figure 50, plate V, 

 with a yolk 95 x 69 and an embryo of 39 mm. In these early stages there is practically no 

 diminution of yolk si2;e. 



To illustrate the slow rate of absorption of yolk, we may consider three large embryos 

 listed by Dean. Thus in Figure 11, plate I, an embryo of 175 mm. (magnified to 205 mm.) 

 sits on a yolk measuring 92 x 89 mm. This was collected April 25. Then "taken about 

 May 1, 1905" were two still larger embryos. The smaller measured 331 mm. in length 

 and had a huge yolk sac measuring 110 x 100 mm. The other is the largest embryo of 

 which there is record. This fish, shown in color in Figure 49, plate V, was 390 mm. 

 (15.35 in.) long and its yolk sac was 100 x 70 mm. in its transverse diameters. 



To recapitulate, Dean's notes will be quoted. The specimens of Oct. 1, 1905, 

 "stage early, probably gastrula", might possibly have grown by "early January" into 

 embryos measuring 11.5, 15.5, and 20 mm. on yolk sacs undiminished in size. But it 

 does not seem Hkely that by "Apr. 25" one of these could have attained the sizie of the 

 l75'mm. embryo of Figure 11, plate I. Nor could the I75'mm. fishlet by "May 1" have 

 grown to an embryo of 390 mm. (yolk 100 x 70), which is represented in Figure 49, plate V. 

 From the above data it is clear that the fish grows much faster than the yolk decreases. 



It is evident that all the yolk must be resorbed before the little shark is thrown out. 

 into the sea to fend for itself. The 15.35'in. fish portrayed in Figure 49, plate V, would be 

 so encumbered in swimming, and the large yolk covered with blood vessels would be so 

 conspicuous and attractive to marauders, that the free life span of the fish would probably 

 be but a few hours at most. But how large would the young shark be when it has used up 

 all the food yolk? Surely it would be much larger — perhaps 20-24 in. (508-610 mm.) 

 long. The latter si2,e is that of a free-swimming Chlamydoselachus taken by the Prince 

 of Monaco at Madeira (CoUett, 1910). But would the uterus of the average-sized female 

 contain such a large "baby" without its being folded or curled up? And could it contain 

 several embryos of this si2,e? 



All the evidence points to a very long period of gestation in Chlaynydoselachus. But 

 how long? Because of its habitat and its breeding throughout the year, it is of course 

 impossible to find the answer in the body or in the habits of the frilled shark. It is 

 practically impossible to ascertain the length of time for the hatching of any shark's egg 

 save in the oviparous forms — and only in those species small enough to be kept in aquaria, 

 where the date of egg-extrusion and of egg-hatching can be recorded. This has been done 

 in terms of "about so many days" for two species of dogfish. One must say "about" for 

 one cannot know how far in development an internally-fertiliz;ed oviparous egg has gone 

 when it is "laid". Here are all the facts, so far as known to me. 



