CRABS AND SHRIMPS, 



211 



for growth in these animais, as in Insects ; in them it is 

 confined to the caterpillar state, in which alone growth 

 takes place ; bnt here it prevails, becanse growth is con- 

 tinued, long after the perfect form is attained. The rigi- 

 dity of the encasing armour forbids the possibility of in- 

 crease in its capacity. The growth, therefore, is periodic. 

 At certain intervals the hard crust is thrown off in several 

 pieces, a new crust having been prepared beneath, which 

 is at first soft, flexible, and expansile. The body, now 

 freed, instantly enlarges in all directions, and, in a few 

 minutes, has attained the full extent of growth needed. 

 The crust at once hardens, and in a brief space becomes 

 as inflexible as was its predecessor, admitting no further 

 enlargement either of its own surface or of the contained 

 organs. The animal usually undergoes this process in 

 the most retired situation it can find, instinctively con- 

 scious of its unprotected condition when soft, and appa- 

 rently feeling sick and feeble. 



Another interesting circumstance in the economy of 

 this Class, and the last we shall at present notice, is the 

 power of renewing injured or lost limbs. If one of the 

 joints of a Crab's leg be wounded, it would bleed to death 

 but for this provision. The animal, however, wisely 

 adopting the saw of " Young Jem" in our nursery-rhyme — - 



" Better lose part than all " — 



stiffens the hurt limb, and suddenly throws it off, the 

 separation invariably taking place at the point where the 

 second joint is united with the first. A small gland is 

 placed here, according to Mr H. Goodsir,* which supplies 



* Ann. of N. EL, vol. xiii., p. 67. 



