EMBRYO WHALE SHARK — GARRICK 5 



I do not know if similar pairs of enlarged denticles occur on the longi- 

 tudinal dermal ridges of adults. However, Ford (1921, p. 493) de- 

 scribed the first denticles to erupt in Scyliorhinus canicula, S. stellaris, 

 and Galeus melanostomus as being conspicuously larger than the nor- 

 mal body denticles and "symmetrically arranged in a sequence of 

 transverse pairs forming two longitudinal rows, one on either side of 

 the midline in a dorsolateral position." At a later stage, these larger 

 denticles "lose their individuality eventually owing to the presence of 

 equally large and similar scales which have grown up around them" 

 (p. 494). 



Teeth. — In the embryo, the teeth are for the most part still covered 

 by membrane, but those that are visible show little difference from the 

 teeth of adults. 



GiLL-RAKERS. — The plankton-sieving apparatus of the adult whale 

 shark consists of transverse cartilaginous bars (representing gill-rakers) 

 which join one gill-arch to the next; these transverse bars are further 

 connected, one to the other, by a secondary grid of slenderer cross 

 members. The entire structure is covered on its internal (pharyngeal) 

 surface by a fine, spongelike lattice or veU derived from dermal den- 

 ticles. This structure forms the sieving apparatus, with interstices 

 1 to 3 mm. in diameter. 



In the embryo the sieve is still in a very early stage of development, 

 comprising only the gill-raker elements. These project forward from 

 each arch to the next, but their tips are still free. On the first arch 

 there are about 26 rakers on the upper limb and 34 on the lower. The 

 rakers are comparatively stout rods, closely arranged, with virtually 

 no space between them. Each raker shows faint indications of being 

 bipinnate, having very short processes developing along the sides. 

 These processes are presumably the rudiments of the secondary grid 

 members. There is as yet no obvious sign of the spongy tissue which 

 will later line their inner surface. 



Reid (1957, p. 157) suggests that the relatively advanced stage of 

 development of the embryo whale shark and the extent to which its 

 external yolk sac has been absorbed are indications that it is approach- 

 ing the size at which it would hatch. This is probably correct. 

 On the other hand, the abdomen is filled almost completely with yolk, 

 forming an oval mass about 80 mm. long, 50 mm. wide, and 40 mm. 

 deep. This yolk supply seemingly would allow sufficient reserve to 

 complete development of the pharyngeal sieve either before or after 

 hatching. Only further specimens will establish whether the juvenile 

 whale shark feeds from the beginning in the same manner as the 

 adults. 



Color and pattern. — The color of the embryo when first 

 removed from the egg-case was "bluish grey with white spots, the 



