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TEXT-BOOK OF ZOOLOGY 



moves through the water by lashing its tail 

 from one side to the other, the fin-membrane 

 being at the same time twisted spirally. 

 (Compare with screw of a steamer. See 

 Greenland whale and fishes.) 



3. Pitxjii ration is carried on through 

 branchiae (see Fishes), which sprout out from 

 the neck in the form of small plumes. Gill- 

 slits lead from the cavity of the throat to the 

 exterior. These external gills, however, soon 

 disappear, being replaced by others formed 

 internally, and protected by a fold of the 

 skin. The water which has been taken in 

 by the mouth flows through the gill- slits, 

 and is again expelled through an opening, 



1, Freshly deposited eggs. 



2, Eggs with the swollen 

 gelatinous envelope. 



3-8, Separate successive 



stages of development. 

 K., branchial aperture. 



Above, a male with vocal 

 sacs ; below, a female in 

 the act of catching an 

 insect. 



«%*5 





'fim»fm 



p 



A 1. - 



KdIIILK FlKKi AND ITS DEVELOPMENT 



X-.. 



