BRIEF SKETCH OF THE TOOTHED WHALES. 93 



Narwhal which he found quiescent, and apparently asleep at 

 the surface with its head immersed, and is of opinion that in 

 Whales respiration is suspended during sleep. As stated, how- 

 ever, in 1885, when the matter was first brought forward at the 

 Aberdeen Meeting of the British Association (where Mr. Gray 

 read his paper), further observations are necessary. Collett* 

 and Lilliet both refer to the views of whalers, who think that 

 after storing their lungs with air the Finners can remain eight 

 or ten hours under water. 



The organs of the circulatory system are so similar in most 

 respects to those in ordinary mammals that they need not be 

 alluded to, save on one point, viz. the presence of numerous 

 spongy networks of blood-vessels {retia mirahilia), such as 

 those in the region of the spine, which by some are supposed 

 to be connected with respiration, but which may also serve for 

 the interchange of material between the lymph and blood, and 

 therefore connected with nutrition ; or the network may supply 

 pure blood to the spinal cord and brain during immersion, and 

 when great pressure on the lungs exists. 



As parts of the digestive system (the next subject for con- 

 sideration), the teeth form a characteristic feature. They are of 

 the kind called " homodont " — that is, nearly alike, the only 

 exception being the Zeuglodonts (of which the skull and vertebrae 

 only are known) of the Eocene period of North America. | The 

 Zeuglodonts, however, differ considerably from the living Toothed 

 Whales — in fact, they hold an intermediate position between the 

 Toothed and the Whalebone Whales. The teeth anteriorly are 

 simple and conical — the first three in the premaxillary, and 

 therefore corresponding with incisors, the next is also simple 

 and conical, but it does not exceed the others in size. Then 

 follow five teeth with two roots, and compressed, pointed, 

 denticulated crowns. The teeth in the Dolphins are held by 

 Kiikenthal and others to belong to the milk-dentition, and 

 therefore that they are truly diphyodont, like most terrestrial 

 mammals. 



* Proc. Zool. Soc. 1886, p. 263. 

 f Ihid., 1910, p. 790. 



I Giebel, Jourdan, and D'Arcy Thompson think Zeuglodonts are allied to 

 Seals and Carnivores, not to Cetaceans. 



