XXV] CETACEA 681 



breathe and eat at the same time enables the mother Whale to force 

 milk down the young one's throat without choking it. 



It is an interesting fact that the nasal organ should have become 

 vestigial in Whales whereas in Fish, it is a large and important sense 

 organ. But we must remember that the nasal organ was originally 

 evolved for the purpose of perceiving substances dissolved in water : 

 but that when land animals were evolved from Fish this organ became 

 adapted to perceive gaseous substances in the air which was drawn 

 past the opening of the nasal organ. Now the Whale is interested 

 in substances dissolved in the water, not in gaseous odours in the 

 air, but as an air-breathing animal it could not admit water to its 

 nasal organ without the risk of choking, and hence this organ has 

 lost its function and become vestigial. 



The external ear is liable to become a great nuisance to an animal 

 which spends so much of its time beneath the surface of the water 

 as every swimmer and diver knows to his cost. Hence in Whales it 

 is reduced to capillary dimensions so as to exclude the water as 

 much as possible. In a Porpoise six feet long, it is of the dimensions 

 of a pin hole. It is certain therefore that Whales do not hear through 

 the outer ear : they hear through the bones of the head as a fish 

 does. This point was made clear by experiments designed to find out 

 the best means of detecting a submerged submarine. 



Whales are divided into sub-orders, the whalebone Whales or 

 MYSTAGOCETI and the toothed Whales or ODONTOCETI. In the 

 latter there are numerous teeth, but they are all alike and simple 

 (Fig. 341), and the maxilla develops a great crest which conceals the 

 orbital plate of the frontal. The great Sperm-whale, Physet&r 

 macrocephalus, of the Southern Seas, has teeth only in the lower jaw 

 and feeds on cuttle-fish and fishes, gripping the long flexible arms 

 of the former by pressing them against the upper jaw. Spermaceti 

 oil is the melted-down fat of this monster. The Ca'ing or Pilot 

 Whale (Globicephalus melas), which also feeds chiefly on cuttle-fish, 

 has teeth on both upper and lower jaws (Fig. 341). Pilot- whales are 

 social in disposition, and the herds are occasionally driven into bays 

 or fiords in the North Atlantic and captured. Smaller toothed 

 Whales are found round the coast of Britain which have teeth in 

 both jaws. Of these we may name the Porpoise, Phocaena, the 

 Dolphin, Delphinus, and the Grampus, Orca. The common Por- 

 poise, Ph. communis, is the most abundant and best known of 

 British Cetaceans. It is not more than six feet long and is often 

 cast ashore. It abounds in the Firth of Clyde. In the Gulf of 

 St Lawrence the White Whale, Delphinapterus leucas, is fairly 

 common. It attains a length of twelve feet. 



