The Embryology of Chlamydoselachus 573 



These encapsuled round eggs have been designated '"unusual" since no one save 

 Dean seems ever to have seen such, but they cannot be termed abnormal. Each seems to 

 have a late blastula on it (these will be considered later) and there is undisputable proof 

 that these round eggs go on to full development. This is admirably shown in Figure 11, 

 plate I. The young fish was 175 mm. long and it is fast to a round yolk sac which in the 

 original drawing measures 92 x 90 mm. and which is now freed of its capsule. Thus this 

 yolk, bearing this advanced embryo, has still the almost perfectly round form of the three 

 eggs shown in Figures 4, 5 and 6, plate I, and, judging by the si2,es of these three other 

 round eggs, it has decreased but little in bulk. 



SIZES OF EGGS OF CHLAMYDOSELACHUS 

 COMPARED WITH THOSE OF OTHER SHARKS 



From his studies of all these extraordinarily large encapsuled eggs of Chlamydo- 

 selachus, Dean drew certain general conclusions as to their size and phylogenetic origin. 

 These conclusions are contained in the only description (a single paragraph) of the eggs of 

 the frilled shark which he ever published (1903). From this, I excerpt the following: 

 ''Chlamydoselachus has specialized in the line of producing large eggs, the largest indeed 

 among recent animals, ostrich hardly excepted [egg 150 mm., 5.9 in., in long diameter]; 

 that it was, however, until recently an egg-depositing shark is apparent from the character 

 of the horn'like capsule (with rudimentary tendrilform processes) which the egg still 

 retains". 



At the time that Dean wrote, the egg of Chlamydoselachus was the largest egg 

 known to him save only that of the ostrich, but since his day larger shark eggs have been 

 discovered. Larger eggs are now known to be carried by various sharks of the family 

 Isuridae, and by the ovoviviparous nurse shark, Ginglymostoma cirratmn, often referred 

 to earlier in this article. The eggs of these sharks will now be described that the reader 

 by comparisons may see how large the eggs of Chlamydoselachus really are. 



SIZES OF EGGS AND EMBRYOS OF THE FRILLED SHARK 



As a basis for comparing the size of the egg of the frilled shark with that of other 

 sharks, it will be necessary to establish the size of this egg. Our earliest information 

 comes from Nishikawa (1898) who had eggs ranging from 102 to 124 mm. in long and 

 from 65 to 75 mm. in short diameter. He also speaks of eggs ''110-120 mm. long". These 

 measurements were presumably made over the egg capsule and its processes. His one 

 figured egg (Text-figure 4) thus measured is 128 x 65 mm., but the yolk mass is only 100 x 

 65 mm. natural size. 



Let us now turn to Dean's materials. The three round eggs (yolks only) measure 

 90 X 87 mm., 96 x 87, and 97 x 88 in the original drawings. His two oblong eggs (yolks 

 only) measure 119 x 80, and 138 x 90. Of his other material, Figure 9, plate I, portrays 

 a 50-mm. embryo on a yolk measuring 108 x 68 mm. Then his Figure 11, plate I shows a 

 large embryo on a yolk sac 92 x 90 mm. Also Dean records an embryo of 331 mm. on 

 a yolk 111 X 100 mm. And finally there is the huge embryo of 390 mm. (15.35 in.) 



