360 FOLLOW THE WHALE 



In the same area where the saro is found, live also those mysterious, 

 complacent, purely aquatic mammals known as manatees. These 

 creatures have lost almost all their hair, except for a pronounced 

 "Old Bill" mustache; their hind limbs have entirely disappeared; 

 their forelimbs are reduced to dwarf arms and their fingers are 

 joined by complete, solid webs, so that, although they can hold their 

 babies to their breasts, they cannot use their forelimbs for much else. 

 Their tails have become curious paddles for going up and down, but 

 these are nothing more than a further development of those of the 

 saro. The next step may be seen in the tail of the manatee's only 

 living relative, the dugong of the Indian Ocean shores. In this beast, 

 these side flaps have been further extended outwards to form tri- 

 angles and have then curved backwards a little at their tips. With 

 this shape of tail, a semirotary, or sculling, motion becomes possible, 

 and this will drive the animal forward as will the propeller of a ship. 



Now, any animal thus driven will immediately tend to be thrown 

 into a rotary motion itself, just as the blades of a helicopter, being 

 forced to go round one way, set the body of the machine going 

 round the other, so that a little additional vertical propeller has to be 

 set in motion on the tail to counteract the effect. The dugong is a 

 comparatively sluggish beast, and can get about slowly without 

 going into a spin. Some whales, however, which are comparatively 

 fast swimmers have encountered this problem and, to counteract it, 

 have developed as stabiHzers a series of fore-and-aft bumps running 

 along the ridge of their backs. The next stage is to be found in 

 the swift dolphins, where perfect stabilizers in the form of tall, 

 triangular dorsal fins hold the beasts steady on their headlong course. 

 The ultimate exaggeration is seen in the predaceous killer, who de- 

 pends on sudden bursts of great speed for swift maneuver. He has 

 truly falcate tail flukes, and an enormous dorsal stabilizer, sometimes 

 over six feet tall and so slender that the tip turns over like the ear 

 of a dog. The purely mechanical evolution of the aquatic mammalian 

 tail, ending in that of the killer, when traced backwards, almost 

 inevitably leads us to a riverine ancestor. 



This alone, however, would mean nothing were it not for other 

 facts discovered by embryologists. As everyone now knows, unborn 

 baby animals go through the whole history of their race from the 

 amoeba to their own father and mother. Not only do unborn whales 



