48 repout — 1877. 



of the dorsal somites to observe that the dermal tissue yielded to the touch 

 and was less resistant than at other times. 



Soon after the animal appears to he restless, and commences to rub its legs 

 one against the other. It then turns itself over on the back, and agitates the 

 whole of the body ; then all of a sudden it bursts the membrane that unites 

 the carapace -with the body, and raises the groat dorsal carapace. 



The animal now rests for a while ; then it recommences by agitating its 

 legs, and moving every part of the body. The carapace is then gradually 

 elevated along the base of the legs, and in less than half an hour the animal 

 is disembarrassed of its old integument. It draws back it head, disengages 

 both its eyes and antennas, then draws out its legs from the case formed of 

 the old integument. 



This latter part of the operation appears to be performed with a great deal 

 of pain, and sometimes in the struggle to liberate the legs from the old skin 

 one or more are broken off. This is probably induced from some incident 

 precluding the external case from being ruptured ; for if the old skin does 

 not split in a longitudinal direction, it is difficult to understand how the logs 

 can bo withdrawn from the old case. But as soon as the crayfish has over- 

 come this painful portion of the moulting, it rapidly disembarrasses itself 

 from the rest of the envelope. It withdraws its head from the carapace, 

 presses forward, and quickly liberates itself from the posterior part, and soon 

 frees itself entirely from the old skin. 



The carapace then falls back into its old relative position, and joins itself to 

 the percion and pleon : thus the old skeleton appears in general form exactly as 

 it did before it was stripped from the animal ; consequently it bears a perfect 

 resemblance to that of a crayfish of the same character. The new skin 

 which succeeds the moulting is soft and membranous ; but in three or four 

 days, or even in twenty-four hours, it becomes encrusted with calcareous 

 matter, and becomes as hard as the old integument. 



Milne-Edwards says that all the higher orders of Crustacea change their 

 skin in nearly tbe same manner. If, he says, we examine a species of Main 

 some time before it has commenced moulting, we shall find between the tost 

 and the chorion a membranous mass that resembles the cellular tissue, im- 

 perfectly condensed at first, but becoming more and more solid and thick 

 as it approaches the period of moulting. 



" This new membrane is evidently," says Milne-Edwards, " secreted by 

 the chorion, and moulds itself upon the test that covers it." We find attached 

 to it nearly every hair that should be present at a later period ; but these 

 appendages are not enclosed within the hairs that are attached to the ancient 

 moult, as Reaumur believed he observed them in the crayfish. Generally 

 they project upon the surface of the new skin, and are folded like the finger 

 of a glove which is inflcctod within itself. 



Collinson, in the 'Phil. Trans.' 1770, art. 51, published some observations 

 on Cancer major, probably the common edible crab. The account which 

 ho gives of the manner in which the animal escapes from the old shell varies 

 from Reaumur's description of the process in the crayfish. 



Instead of the carapace being raised as a whole and thrown off perfect, it 

 divides along the lateral sutures that extend from the anterior portion of the 

 mouth to the posterior margin of the carapace. This, according to Milne- 

 Edwards, separates the lateral pieces (or epimera) from the dorsal piece, or 

 somite proper ; but, according to Dana and myself, the line of division sepa- 

 rates the second antennal and mandibular somites. 



