690 



MANUAL OF ZOOLOGY. 



is blunt, and is not produced into a projecting muzzle. The Porpoise 

 frequents the Atlantic, Pacific, Mediterranean, and Arctic Oceans, and the 

 North Sea, and is commonly seen off our coasts. Another British species is 

 the Grampus (Orca gladiator] , but this is much larger, attaining a length 

 of from eighteen to twenty feet. Nearly allied to the Grampus is the so- 

 called ' ' Caing " Whale, or, as it is sometimes termed, the Bottle-nosed 

 Whale (Globicephalus melas or Phoc&na globiceps). This species occurs not 



Fig. 386. The common Dolphin (Delphinus delphis). 



uncommonly round the Orkney and Shetland Islands, and attains a length 

 of as much as twenty-four feet. It is gregarious in its habits, and is often 

 killed for the sake of its oil. 



Closely allied to the true Dolphins are some curious Cetaceans, belonging 

 to three genera, but all inhabiting fresh waters. One of these is the Gan- 

 getic Dolphin (Platanista Gangetica), which inhabits the Ganges, especially 

 near its mouth. This singular animal is characterised by the great length 

 of its slender muzzle, and by the small size of the eyes. It attains the 

 length of seven feet, and the blow-hole is a longitudinal fissure, and there- 

 fore quite unlike that of the -typical Delphinidce. Closely allied to this, or 

 identical with it, is the Platanista Indi of the Indus ; while the Orcella 

 fluminalis inhabits the Irawaddy. Another fresh-water form is the Inia 

 Boliviensis, which inhabits the rivers of Bolivia, and is found at a distance 

 of more than two thousand miles from the sea. Lastly, the Pontoporia 

 Blainvillii is a small Dolphin which inhabits the rivers of the Argentine 

 Republic and of Patagonia. 



The last of the Delphinidtz is the extraordinary Narwhal or Sea-unicorn 

 (Monodon monoceros). The Narwhal is an inhabitant of the arctic seas, 

 and attains a length of as much as fifteen feet, counting in the body alone. 

 The dentition, however, is what constitutes the great peculiarity of the 

 Narwhal. The lower jaw is altogether destitute of teeth, and the upper 

 jaw in the females also exhibits no teeth externally, as a general rule at any 

 rate, though there are two rudimentary canines (often looked upon as in- 

 cisors) which do not cut the gum. In the males, the lower jaw is likewise 

 edentulous, but the upper jaw is furnished with two molar teeth concealed 

 in the gum, and with two canines. Of these two upper canines, that of 

 the right side is generally rudimentary, and is concealed from view. The 

 left upper canine, on the other hand,, is developed from a permanent pulp, 

 and grows to an enormous size, continuing to increase in length through- 

 out the life of the animal. It forms a tusk of from eight to ten feet in 

 length, and it has its entire surface spirally twisted. As an abnormality, 

 both the upper canines may be developed in this way so as to form pro- 

 jecting tusks ; and it is stated that the tusk is occasionally present in the 

 female. The function of this extraordinary tooth is doubtless offensive. 



