2g8 



TEXT-BOOK OF ZOOLOGY 



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

 spots near their banks (see salmon). The skeleton is cartilaginous (see 

 sharks), and receives additional strength from bony plates or scutes 

 developed in the skin. These scutes possess a superficial coating of solid 

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

 the elongated body. The caudal fin is asymmetrical (heterocercal) as m 

 the sharks. The fish seeks its food in the mud and sand, using its four 

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

 its head into the bottom. The food consists 

 chiefly of worms, insect larva? and small fishes. 

 The mouth, which lies upon the under surface of 

 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 stur- 



Stupj;eox. (About one-til'tietli natural size.) 



geon and closely related species the delicacy known as caviare is 

 prepared. 



The best caviare (Russian 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 hansm- 

 bhiKr = sturgeon's bladder. 



