THE CRAYFISH AND ITS ALLIES 103 



moulting, or casting off the entire shell at intervals, is 

 attended with great dangers to the lobster, since the animal 

 is so soft bodied as to J)e able to offer little resistance to 

 its enemies. 



The moulting process in the lobster, crayfish, and other 

 Crustacea is made necessary from the fact that these animals 

 are enclosed in a chitinous covering which is impregnated 

 with salts of lime. It is evident that an animal cannot 

 increase in size while so encased ; hence special provision 

 for growth has to be made by the moulting or casting off 

 of the hard shell. This process is accomplished in the 

 following manner: previous to the throwing off of the old 

 skin a new soft one is formed inside, the lime is absorbed 

 from the old shell in a dorsal line along the carapace, 

 reaching from the rostrum to its posterior margin. Ab- 

 sorption also takes place at the joints of the limbs. When 

 the lobster has attained this stage it is dark in color, and 

 known by fishermen as the " black lobster." The carapace 

 now splits along this dorsal median line of absorption, the 

 blood leaves the limbs, which are thus made flabbier, and 

 by involuntary muscular movements they are drawn, large 

 claw and all, through the joints of the old shell. The 

 anterior portion of the body is first drawn out through the 

 dorsal rent, and lastly the tail. Not only is the entire outer 

 covering cast off, but the lining of the oesophagus, stomach, 

 and intestine as well, since these organs are formed by an 

 infolding of the skin. By means of the return of the blood 

 to the limbs and rapid absorption of water, the body of the 

 lobster soon swells to a size far beyond that of the old shell. 

 There remains in the stomach, after moulting, a calcareous 

 nodule which has long been known by the name of "crab's- 

 eyes." These " crab's-eyes " were formerly much sought 



