Mr. C. Spence Bate's Notes on Crustacea. 299 



of the future shell, which process commences previously, and is 

 completed after the removal of the exuviae. 



Shedding the Eocuviae. 



VI. The manner in which the crab seems to free itself of its 

 extraneous covering is by the internal growth of the animal : 

 the increased bulk acting upon the principle of a lever, the 

 transverse growth becomes compressed within the limits of the 

 old carapace, which induces an increase of dimension in the 

 contrary direction, and the first sign which I have noticed of 

 the approaching change in the animal's oeconomy is an increase in 

 its thickness, whereby the sections of the abdomen become more 

 conspicuous from above * ; as this increases the crab wanders 

 about in search of a retired spot, and often becomes very savage, 

 darting at anything which approaches it, until at length the 

 moment draws near, when it hitches the point of one of its claws 

 in some crack or crevice, and withdraws itself from its old skin, 

 escaping between the carapace and abdomen. The moment it 

 becomes free, the full size to which it grows, until it again throws 

 off the shell, is attained. 



I cannot help here remarking, in I'eference to a case mentioned 

 by Reaumur, who watched the crayfish {Astacus fluviatilis) throw 

 off its shell — he says the process was one of great labour and 

 difficulty as well as of long duration — in all the cases which I 

 have watched, the process was easily and quietly done, in a short 

 period of time and without any struggle. One only exception 

 have I to make, and that was in a crab which I frequently took 

 into my hands, and cut away the carapace with a pair of scissors 

 as it was loosened ; after the animal had freed itself from the 

 exuviae it hung by the eye-stalks, nor could the animal be free of 

 them without assistance, a circumstance which makes me imagine 

 the anterior portion is removed by force applied to the carapace 

 by the legs of the animal. 



They seem to have the power of retaining their shell at will, 

 until suitable circumstances both as to time and place occur for 

 casting it with security, for in many instances I have seen them 

 both before and even after the process has commenced, and 

 patiently watched for hours at a time without success, yet upon 

 returning after a few minutes' absence I have found the exuviae 

 shed. 



When they have thrown off the old skeleton they are very 

 liable to become the prey of larger animals both of their own and 

 other species, of which they themselves seem to be aware, and 



* These observations were made upon the common littoral crab, Carcinus 

 Manas. 



