150 CRUSTACEANS. 



motionless, contracted, and supine, until the dread of danger is dispelled, 

 their natural posture and functions are resumed. Here are recognised 

 decisive features of insects. 



Although we characterise the Crustaceans in general as invested by 

 a hard shell, this is not strictly true of every species. The integument 

 of some is rather horny or coriaceous, capable of slight resistance in its 

 place, and yielding easily to pressure when separated. Perhaps it gra- 

 dually degenerates into an integumentary skin. 



For practical illustration of the general form and nature of the 

 Crustacean tribes treated of in this work, the subject may be conve- 

 niently subdivided into three portions, comprehending 

 I. Cancer, the Crab. 



II. Astacus, the Lobster. 



III. Miscellaneous subjects, some of them approaching both, or re- 

 sembling neither, nor alike familiar or sufficiently understood. 



PART I. 

 A. DECAPODES, TEN-LIMBED, SHORT -TAILED CRABS, BRACHYURI. 



1. CANCER JLENAS The Shore or Harbour Crab. Plates XXXIV., 



xxxv., xxxvi., xxxvn. 



A small green Crab, running actively over the rocks and sands 

 during recess of the tide, cannot have escaped the notice of those fre- 

 quenting the sea-shore. 



This is the subject of the present paragraph ; and as it is one 

 equally convenient for experiment and observation, especially from its 

 size and abundance, we shall view it at greater length than many other 

 species require. 



Though usually green, it is seen under various aspects, whether 

 entire or mutilated. The green is uniform, or interrupted ; of various 

 shades and intensity, sometimes variegated in such a manner, that the 

 shell seems green and black. But plain and uniform green must be 

 considered the usual and more natural colour. 



