84 WHALES 



Figure 4!). Dorsal view of the head of a 3 feet g inch Fin 

 Whale foetus^ showing fwsition of tactile hairs in relation 

 to eyes and blowhole. 



Since we are on the subject of the external appearance of whales, we 

 must not forget to mention their colour. A number of species - Right 

 Whales, Sperm Whales, Pigmy Sperm Whales, Bottlenose Whales, False 

 Killers, Pilot Whales, Gangetic Dolphins, and Indian Porpoises - are 

 practically black, though in most of them the black shades off into dark 

 grey on the ventral side. The Beluga is creamy white, and the Narwhal 

 is yellowish with dark grey or blackish spots on the back, the colour 

 becoming markedly lighter on the ventral side. The same is true of the 

 Grey Whale, of Risso's Dolphin, and of the Blue Whale. All other 

 Rorquals and most other Odontocetes, i.e. most Dolphins, are black on 

 the dorsal and white on the ventral side. In some cases, e.g. the Common 

 Dolphin, the black is relieved by brown or violet shades, and there may 

 be light spots on the black, or dark spots on the white surface, but, on the 

 whole, black and white are the predominant colours and the transition 

 from one to the other is gradual. 



Now the same distribution of colour - dark on top and light beneath - 

 can also be found in most fishes, in seals, penguins, and in a great number 

 of terrestrial animals. It has a clear biological significance, for it serves as 

 an excellent means of camouflage - countershading. This is best illustrated 

 by means of a model. If light is allowed to fall perpendicularly on a 

 grey cylinder held horizontally in front of a grey screen, the cylinder 

 will not merge with the screen but be clearly visible, since the light will 

 illuminate its upper surface, while the cylinder's own shadow will darken 

 its lower part. Now, if we colour the cylinder dark on top and whiten it 

 beneath, the two colours will merge imperceptibly, for less light will be 

 reflected from the top and more from the bottom. The cylinder will fuse 

 into the background. Countershading enables animals to hide both from 

 their pursuers and their prey. Amongst the Cetaceans there is, however, 

 an exception to the general rule of countershading, viz. Cuvier's Beaked 



