I30 DISCOVERY REPORTS 



back in the bent position thus taper until the tip — not of the tail — but of the fin is reached, and as 

 they submerge together, the whole sinks obliquely forwards with remarkably little disturbance to the 

 water. 



The caudal peduncle should be considered together with the dorsal fin because it seems to share the 

 same function and has similarity of shape. Its structure has been frequently misrepresented (Scammon, 

 1874, p. 37 and plate 11, fig. 2; True, 1904, plate 48, fig. i ; Millais, 1906, plate 59, figs. 2, 3 ; Lillie, 

 1915, plate VII, fig. I ; Allen, 1916, plate 10, etc.). 



Fig. 6. Diagrams illustrating the posture of Fin whales swimming at high speed. 



The point in need of particular emphasis, is the insertion of the flukes on the peduncle. The majority 

 of authors have shown the plane of the flukes to lie more or less midway between the dorsal and ventral 

 contours of the peduncle, whereas in fact it is very distinctly nearer the ventral edge. In Fig. 7 a, 

 which is based on photographs published by True (1904, plate 11, fig. 4 and plate 14, figs, i, 2), 

 two-thirds of the peduncle are shown dorsal to the plane of the flukes and in southern Blue and Fin 

 whales it is approximately the same (Plate XXXIII, fig. 6; Fig. ^b). Collett (1886, plate XXV, fig. i) 

 and Olsen (191 3, plate CXI, fig. 7) have respectively shown the same thing for the Sei whale and 

 Bryde's whale. 



dorsal edge 



/ 



caudal 

 peduncle 



notch of 



fluke 



rigint fluke 

 nr (sectioned) 



dorsa 

 ed ge of 

 peduncle 



sft fluke (sectioned) 



Q 



L left fluke 



'^ (sectioned) 



Fig. 7. Diagrams of the caudal peduncle, a, viewed from the left side {Balaenoptera viusculus, from True, 1904). b, viewed 

 from behind and from the right side, as in Plate XXXIII, fig. 6 {B. physalus). 



When whales dive at unusually steep angles they submerge the fin before the peduncle and the 

 streamline form of the latter in transverse section is then seen to best advantage. By its great depth — 

 4 ft. in a 65 ft. whale (Howell, 1930, p. 204) — the flukes are kept well beneath the surface as long as 

 possible. 



In considering the eflFects of the flattened head and its mobility, the streamlined dorsal fin and the 

 caudal peduncle, it would be interesting to know more about the habits of other whales. The Right 

 whale is also a plankton feeder and visits the surface to breathe but is said to be slow in its movements. 

 In this whale the maxillae are laterally narrow and dorsoventrally curved ; mobility of the head is 

 reduced by extensive fusion of the cervical vertebrae and it has no dorsal fin. Killer whales and dol- 

 phins which feed upon active prey have very much larger dorsal fins placed farther forward. The 



