216 POPULAll HISTORY OF THE AQUARIUM. 



the only means of saving him. But how fares it with Crabs 

 and Lobsters, who have no doctors nor scissors ? The strange 

 fact is, that they have the power of bursting then- shell, 

 withdrawing from it, leaving every part perfect as before, 

 but empty. The eyes, feelers, mandibles, all the delicate 

 members which have been covered by shell, even if in- 

 ternal, are all withdrawn from their sheaths, and the whole 

 collection of sheaths remains as one whole and entire in- 

 vestment, cast off. 



You may place a Shrimp in a vase by himself, you may 

 leave him unobserved for a time; on returning, behold 

 there are two ! No : one, though perfect in shape, is " in 

 substance unsubstantial " it is a ghost, a transparent empty 

 integument, which forms the "alter ego'' of the Shrimp. 

 Even while still invested by the covering now thrown off, 

 the Shrimp had been prepared for a change by tjie gradual 

 formation of a new one underneath the old ; and this new 

 one, although soft when first exposed by the sloughing of 

 the other, soon becomes as hard as its predecessor, and far 

 more bright. 



In some of the higher forms, the exuviation takes place 

 annually with regularity, the size increasing in each moult. 

 In other forms it is a much more frequent phenomenon. 



