XII. 



THE FEESH-WATER CEAYFISH {Astacus flu- 

 viatilis) AND THE LOBSTER (Homarus vul- 

 garis). 



The Crayfish and the Lobster are inhabitants of the 

 water, the former occurring in' many of our rivers and the 

 latter abounding on the rocky parts of the coasts of the 

 European seas. They are bilaterally symmetrical animals, 

 provided -with many pairs of limbs, among which the 

 large prehensile 'claws' are conspicuous. They are very 

 active, walking and swimming with equal ease and sometimes 

 propelling themselves backwards or forwards, with great 

 swiftness, by strokes of the broad fin which terminates the 

 body. They have conspicuous eyes, mounted upon moveable 

 stalks, at the anterior end of the head; and two pairs of 

 feelers, one pair of which are as long as the body, while the 

 other pair are much shorter. 



The body and limbs are invested by a strong jointed 

 shell, or exosJceleton, which is a product of the subjacent 

 epidermis, and consists of layers of membrane which remain 

 soft and flexible in the interspaces between the segments 

 of the body and limbs, but are rendered hard and dense 

 elsewhere by the deposit of calcareous salts ; the exoskeleton 

 is deeply tinged with a colouring matter which turns red 

 when exposed to the action of boiling water. The body pre- 



