248 



FIRST LESSONS IN ZOOLOGY. 



r-/ 



over, the tail is fluked horizontally to enable it to dive to 



enormous depths. 



The external nostrils 

 are either single or dou- 

 ble, and are situated on 

 the top of the head; they 

 are modified to form the 

 spiracles or "blow- 

 holes ;" certain folds of 

 the skin prevent the 

 water from entering the 

 air-passages. The vapor 

 blown from the holes 

 does not consist of water, 

 but of the mucus from 

 the nostrils, and the 

 moisture in the breath. 

 The blow-holes vary in 

 form in different kinds 

 of whales. The "spout" 

 of the sperm whale issues 

 in a single short stream 

 from the extreme end of 

 the snout, and curls over 

 in front of the head ; that 

 of the fin-back whale 

 forms a single column of 

 vapor about ten feet li iii b ; 

 the right, humpback and 

 sulphur - bottom whales 

 each ' ' blow" in a double 

 stream, which is directed 

 backward towards the 

 tail. 



Whales are rarely over 

 fifty feet long; the sperm- 

 whale has been known to reach a little over twenty-three 



