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TEXT-BOOK OF ZOOLOGY 



UP the rivers for the purpose of depositing its eggs on shallow sandy 

 its near their banks (see salmon). The skeleton is cart, agmous (see 

 harks and receives additional strength from bony plates or scutes 

 devX'ed in the skin. These scutes possess a superficial coating of solid 

 enlmel and are disposed on the top of the head, and m five rows down 

 theTongated body The caudal fin is asymmetrical (heterocercal as m 

 he shaTs The fish seeks its food in the mud and sand using its four 

 XTas tactile organs in the search (compare tench and shad), or boring 

 its head into the bottom. The food consists 

 chiefly of worms, insect larvse and small fishes. 

 The mouth, which lies upon the under surface ot 

 the head, is toothless and protrusible, and there- 

 fore serves, as in the Teleostei, as a prehensile 

 organ (see p. 271). From the roe of the star- 



STURGEON. (About one-fiftieth natural size.) 



geon and closely related species the delicacy known as caviare is 

 prepared. 



The best caviare (Eussian or Astrakhan) is prepared more especially 

 from the Russian Sturgeon (A. huso) which inhabits the Black and 

 Caspian seas and the rivers which discharge themselves into them. This 

 species may attain to a length of 30 feet. From the air-bladders of 

 sturgeons is made isinglass, a word derived from the German hausen- 

 blasc = sturgeon's bladder. 



