AQUATIC MAMMALS 105 



be desirable to wait for a more exhaustive examination of a large 

 series of individuals before absolutely pronouncing them to be 

 specifically identical. There is nothing yet known by which we can 

 separate the "Humpback Whales" (Megaptera) of Greenland, the 

 Cape of Good Hope, and Japan. The same may be said of the 

 common Dolphin of the European seas (Delphinus delphis) and the 

 so-called D. bairdi of the North Pacific and D. forsteri of the 

 Australian seas. The Pilot Whale (Globicephalus melas) and the 

 Pseudorca of the North Atlantic and of New Zealand are also, 

 so far as present knowledge enables us to judge, respectively alike. 

 Many other similar cases might be given. Captain Maury collected 

 much valuable evidence about the distribution of the larger Cetacea, 

 and, finding Right Whales (Balcena) common in both northern and 

 southern temperate seas, and absent in the intermediate region, laid 

 down the axiom that " the torrid zone is to the Right Whale as a sea 

 of fire, through which he cannot pass." Hence all cetologists have 

 assumed that the Right Whale of the North Atlantic (B. Uscayensis), 

 that of the South Seas (B. australis), and that of the North Pacific (B. 

 japonica), are necessarily distinct species. The anatomical structure 

 and external appearance of all are, however, so far as yet known, 

 marvellously alike, and, unless some distinguishing characters can 

 be pointed out, it seems scarcely justifiable to separate them from 

 geographical position alone ; as, though the tropical seas may be 

 usually avoided by them, it does not seem impossible, or even 

 improbable, that some individuals of animals of such size and rapid 

 powers of swimming may have at some time traversed so small a 

 space of ocean as that which divides the present habitual localities 

 of these supposed distinct species. If identity or diversity of 

 structural characters is not to be allowed as a test of species in 

 these cases, as it is usually admitted to be in others, the study of 

 their geographical distribution becomes an impossibility. 



Although many species are thus apparently of such wide dis- 

 tribution, others are certainly restricted ; thus the Arctic Right 

 Whale (Balcena mysticetus) has been conclusively shown to be limited 

 in its range to the region of the northern circumpolar ice, and no 

 corresponding species has been met with in the southern hemisphere. 

 In this case, not only temperature, but also the peculiarity of its 

 mode of feeding, may be the cause. The Narwhal and the Beluga 

 have a very similar distribution, though the latter occasionally 

 ranges farther south. The common Hyperoodon is restricted to 

 the North Atlantic, never entering, so far as is yet known, the 

 tropical seas. Other species are exclusively tropical or austral in 

 their range. One of the true Whalebone Whales (Neobalcena 

 marginata) has only been met with hitherto in the seas round 

 Australia and New Zealand; and a large Ziphioid (Berardius 

 arnouxi) only near the last-named islands. 



