DOLPHINS AND SIRENS. 49 



But, inasmuch as only the male possesses the horn, 

 and the female needs food quite as much as the other 

 sex, it is evident that she would die of starvation if the 

 horn were necessary in procuring food. Another theory 

 is, that when the narwhal gets below an ice-field, and 

 wishes to breathe, it bores holes through the ice with 

 its horn. But this theory is open to the same objection 

 as the former, the females wanting to breathe as well 

 as the males, and yet having no horn. Moreover, I do 

 not think that any narwhal could drive its tusk through 

 the enormously thick and hard-frozen ice of the 

 Northern waters in which it lives. It would be 

 much more likely to break the tusk than to pierce 

 the ice. 



No use has been observed for this extraordinary 

 appendage, but the very fact that it exists is a proof 

 that it must serve some definite and important purpose, 

 It has already been mentioned that, as a rule, only one 

 tusk is developed. Several specimens have been dis- 

 covered, in which both have been developed. It is 

 remarkable that in each case the animal was a 

 female. 



A very remarkable instance of a mammalian Water 

 Trespasser occurs in India. It inhabits the Ganges, 

 and is called the Susue,or Soosoo (Platanista Gangetica). 

 Perhaps the reader may remember that the same river 

 is also inhabited by a peculiar crocodile, which has a very 

 long, narrow snout, widened and flattened at the end. 

 The susue imitates this lizard in the most singular 

 manner. Like the crocodile, the susue has a very long 

 and narrow snout, on account of which some zoologists 

 have called it Delphinus restrains. 



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