EMBRYO WHALE SHARK — GARRICK 3 



only ail apparent difference for the following reason. The dorsal lobe 

 of the caudal fin of the embryo is raised only slightly from the 

 horizontal axis of the body; hence, the posterior margin between the 

 dorsal and ventral lobes is deeply notched, the angle being less than 

 90°, In the adult the caudal fin is lunate, the dorsal lobe being raised 

 steeply from the horizontal axis, with the result that the posterior 

 margin is only slightly concave. It follows that the change leading 

 from the slightly raised dorsal lobe in the embryo to the steeply 

 raised lobe in the adult woidd yield relative total lengths which are 

 not strictly comparable, and thus this difference woidd provide bias 

 in proportional lengths of structures, such as head length, if calculated 

 in terms of the total length. Accordingly, one would expect the head 

 length of the embryo to have a lower relative value in terms of total 

 length than is the case for the adult. Better comparison is afforded 

 by examining the head length in terms of the length to the upper 

 caudal origin — this shows the relative head length in embryo and 

 adidt to be the same, which is nearer to the actual situation in most 

 other sharks. 



The need for caution in extrapolating proportional dimensions of 

 small specimens is demonstrated by the different growth rates oper- 

 ating on the first dorsal fin of the embryo as compared with the second 

 dorsal and anal. Dimensions of the first dorsal fin in the embryo 

 and in the adult indicate that the rate of vertical growth is proportion- 

 ately faster than that of horizontal, whereas in the second dorsal 

 and anal fins the horizontal growth is faster. A similar situation 

 has been described for Etmoptertis baxteri Garrick (Garrick, 1960, 

 p. 548) and it may be relatively common. The lengths of the free 

 rear tips of the dorsal and anal fins compared with theh bases also 

 show considerable change with growth. In the embryo, these free 

 tips are relatively short (about 4.0 in base in the first dorsal fin) but 

 in the adidt they are much longer (about 1.4 in base in the first dorsal). 

 Another change affecting the comparison of all fins is the usual 

 tendency for fin tips to become relatively pointed in the adidt, whereas 

 in the embryo they are more rounded or blunt tipped (V. G. Springer, 

 1961, p. 480, gives an example of this in Mustelus norrisi Springer). 

 The tip of the dorsal lobe of the caudal fin in the embryo is distinctly 

 notched, presumably representing the subterminal notch, which is 

 not evident in the adult. 



Dermal ridges. — As noted by Reid (1957, p. 158), the embryo 

 whale shark has a longitudinal dermal ridge originating on each side 

 of the head and dividing, above the end of the pectoral fin, into two 

 ridges which continue posteriorly. Reid identified this ridge as one 

 corresponding to an upper divided ridge in the adult. Tiie adult 

 has, in addition, a lower ridge which extends the whole length of its 



