CRUSTACEA. 303 



lations of calcareous matter, situated at the sides of the stomach, 

 and known in the old pharmaceutical works as " Oculi Cancrorum," 

 have disappeared: it would seem that the hardening material had been 

 previously accumulated in readiness for the rapid calcification of the 

 new crust, in order to reduce to the shortest period the defenceless 

 state of the craw-fish after its moult. 



The chief difficulty in accepting this account of the moult has 

 been with regard to the possibility of the soft parts filling the ex- 

 panded segments of the pincer-claws of the crab or lobster being 

 withdrawn through the narrow apertures of those segments where 

 they are joined together. But the whole muscular system of the 

 moulting Crustacean is subject at that period to active absorption, 

 which reduces it to about a third of what the cavity is capable of 

 containing. A quantity of sea-water is introduced between the 

 shrunken soft parts and the old hard shell. This interposed fluid 

 stretches every part of the yielding walls of the joints, and facilitates 

 the passage of the reduced muscular structure through the contracted 

 apertures. The limbs are subject, in the act of extrication, to 

 spasmodic twitchings ; but, when a small portion of the soft claw 

 has been thus withdrawn from the orifice, the rest follows almost 

 without an effort. 



In shedding the main part of the shell or carapace, the line of 

 union round the sides and front, which passes between the eyes and 

 mouth, and terminates on each side near the insertion of the hinder 

 legs, is dissolved by absorption. The lining membrane of the old 

 shell, which is the basis of the formation of the new, is reflected 

 into each hard compartment lodging the muscular masses, and into 

 the chambers for the stomach and other soft parts : by the changes 

 it undergoes in the preparation for calcification it cuts off the former 

 close connection of the included parts with the apodemata and 

 manifold processes of the old complex shell. In the act of sepa- 

 ration the crab has sometimes been seen to throw itself on its 

 back, working the branchiae with unusual force, and making the 

 utmost effort to disengage the internal processes. It escapes at the 

 fissure where the tail is connected with the carapace. Sometimes the 

 crab hitches one of its claws into some crack or fissure, and from this 

 point of resistance gains more power in emerging and withdrawing 

 itself from between the carapace and tail. The parts of the old crust 

 once evacuated, fall by the elasticity of their joints into their natural 

 relative position : even the line around the carapace does not appear 

 separated unless minutely examined ; while the antennae, palpi, 

 eyes, complicated organs of the mouth, branchi^, internal tendons, 

 inner membrane of the stomach, with the gastric teeth, the double 

 % 



