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. forstert 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 (Balena) 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. biscayensis), 
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 (Balena 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 Hyperoddon 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 (Neobulena 
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. 
