CRABS AND SHRIMPS. 
211 
for growth in these animals, as in Insects ; in them it is 
confined to tho caterpillar state, in which alone growth 
takes place ; but hero it prevails, because 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. Tho 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 II. Goods ir,* which supplies 
Ann. of N. IT., vol. xiii., p. 67. 
