378 Appendix C 



of cetacean morphology presents a wide field for study that would well 

 warrant investigation. 



There are species that display the most exaggerated tail-fluke forms, 

 notably the gray whale wherein the forward edge is concave on either 

 fluke and the hind edge widely convex, so that the whole is fan-shaped 

 with a deep central notch. This may be an ultimate development of the 

 main evolutionary trend that is depicted in the accompanying chart; it 

 might equally well have been developed very long ago from quite an- 

 other line of change stemming almost directly from the paddle of the 

 manatee stage. The susu, and to some extent also the boutu, has a tail 

 that appears to be at least partially collapsible, more like the combined 

 hind flippers of a seal, but this again may be an offshoot of the main 

 trend, which would appear to be as shown in the chart. 



While the side flaps, or flukes, were widening and ever retreating, 

 their combined hind edge appears to have become, first, convex, then, 

 straight, and finally, concave. From this point on, a form of fluting set 

 in, starting with the backward extension of two flaps immediately to 

 either side of the central point, which remained static and thus caused 

 a notch. Such a condition is seen in its primitive form in the tail of the 

 boutu. By further development of this trend, we reach the fluke form of 

 many oceanic dolphins, notably that of the killer, in which the median 

 notch is very deep. When we come to the rorquals, we encounter a 

 further complexity in the development of an additional pair of convexi- 

 ties on either side of the hind edge of the combined flukes, and the ulti- 

 mate form appears to be that found in the humpback, where, by redupli- 

 cation, these convexities and intervening concavities have produced 

 an irregular fluting, or slotting, comparable to that developed by aero- 

 nautical engineers on the hind edge of the wing of certain airplane 

 models. 



The whole development is undoubtedly a mechanistically controlled 

 reaction to ever increasing speed and maneuverability. It must be borne 

 in mind that the drive of a whale is transmitted from the enormous 

 muscles within the tail proper, which lies inside the body ahead of the 

 flukes, to the water via a most remarkable semirotary, or sculUng, action 

 of the flukes. While the "tail" appears simply to go up and down as a 

 whole, each fluke bends once, twice, or even more times along its fore- 

 aft axis at each stroke, and the right fluke has an exactly opposite cycle 

 to that of the left. The motions are enormously complicated, quite im- 

 possible to describe in text, and so fast they can hardly be seen with the 

 naked eye even in the clearest water and at close range. The net result, 

 however, is that every part of the surface of both tail flukes, above and 



