XXV] CETACEA 683 



or strainer. After the Whale has taken water into its mouth it 

 raises its tongue against the edges of the plates and allows the 

 water to trickle out through the strainer described above ; all the 

 small animals taken in the water are thus retained and then 

 swallowed. The best quality of whalebone is obtained from the 

 Right Whale, Balaena mysticetus, an animal about 50 feet long, 

 found only in the Arctic regions. The Great Rorqual Whale, 

 Balaenoptera sibbaldi, has a fin in the middle of its back, and 

 attains a length of 60 80 feet ; it is the largest animal now 

 found on the globe and is very abundant. The Lesser Rorqual, 

 Balaenoptera rostrata, is a smaller animal some 30 feet in length. 

 On two occasions at least the animal has strayed up the St Lawrence 

 as far as Montreal where it has been starved to death in fresh water. 

 The head of Balaenoptera is much shorter than Balaena and the 

 whalebone is shorter and coarser. 



In Eocene deposits remains of primitive toothed Whales are found 

 which have been termed " Zeuglodonts," because the teeth have two 

 distinct roots and were at first mistaken for two teeth fused together, 

 hence the name (Gr. ^evyXry, loop of a yoke ; 68ovs, oSoVrcs, teeth, lit. 

 yoked-teeth). The teeth were distinguishable into incisors, canines 

 and trenchant cheek-teeth like the premolars of the Dog. These 

 remains give reason to believe that the land-mammal from which 

 Cetaceans were derived was a member of the group Creodonta an 

 extinct group which might be described either as primitive Carnivora 

 or as intermediate between Insectivora and Carnivora. This group 

 was distinguished by the possession of small incisors, large canines and 

 trenchant cheek-teeth carrying three cusps like those of primitive 

 Insectivora but no carnassial teeth were differentiated. It is quite 

 possible that Seals (Carnivora Pinnipedia) are likewise directly 

 derived from Creodonta since they also have no carnassial teeth. 

 In this case Whales and Seals would represent two independent 

 adaptations of primitive Carnivora to aquatic life, but the means by 

 which the adaptation was effected are totally different in the two 

 cases, for the hairy coat of Seals is functionally replaced by the 

 blubber of Whales whilst the powerful tail fin of Whales is represented 

 by the hind-legs of Seals. 



Order VL Ungulata. 



The great group of the Ungulata or hoofed animals represents 

 the second line of evolution from the primitive Insectivora. Here 

 we find that all power of grasping with the limbs is absent and the 



