THE AMERICAN LOBSTER. 87 



repeated by Eymer Jones (106) and others. It is, without doubt, erroneous, but 

 possibly based originally upon an exceptional occurrence. 



At the time of the casting of the shell the large claws must be practically free 

 from blood, since, as Vitzou has pointed out, if the claw were to be increased in size 

 it would be next to impossible for it to be withdrawn without rupture. The older 

 naturalists used to explain the withdrawal of the large claws by a wasting of the 

 tissues. The lobster was supposed to become sick and emaciated, which, of course, 

 was an error. The most significant fact in this process is the displacement of the 

 liquids which normally belong to these appendages. 



Couch (47), in his account of the exuviation of the common edible crab of Great 

 Britain, Cancer pagur us, maintains that the membranes in the areas of absorption at 

 the base of the chelipeds split along the edges and open like hinges, thus freeing 

 the limb from its constraint. This does not happen in the lobster, as Couch inferred, 

 and even if it did no benefit would arise, since there is the unbroken ring of the 

 coxopodite, through which the tissues must still pass. Spence Bate (10) thought that 

 the splitting of the walls of the cheliped, alluded to by Couch, might be to enable "the 

 animal to withdraw the great osseous tendon." It is difficult to understand what is 

 here meant. The great osseous tendons are never withdrawn at all (past the absorp- 

 tion areas at the base of the limb), but remain attached to the old shell, of which they 

 form a part. 



THE CAST-OFF SHELL. 



At the time of the molt there is an intermediate membrane which makes its 

 appearance between the new and old shells. It is non-cellular, has a gelatinous appear- 

 ance, is very transparent, and may be found adherent to the old shell after the molt is 

 past. When examined microscopically it has the appearance shown in fig. 177, pi. 44. 

 It bears the impress of a mosaic of cells, which can be none other than the cells of the 

 chitinogenous epithelium. Vitzou is thus in error in supposing that this substance is 

 a secretion of the chitinogenous epithelium underlying the new carapace, which it 

 traverses by endosmosis. It must be either the first secreted product of the new shell 

 or the innermost layer of the old shell modified by absorption. 



In this cuticular membrane the parts which correspond to the cell boundaries (of 

 the chitinogenous epithelium) have the form of elevated ridges on the under side, and 

 m the center of each polygonal area there is a slight thickening. Beauinur (162) had 

 in view a similar structure in the crayfish when he spoke of a glairy matter, "as 

 transparent as water, which separated the parts which the crayfish was soon to 

 cast oft' from the rest of the body, and which allowed these to glide smoothly over one 

 another." 



There is normally no rupturing of the shell in any part in the course of the molt. 

 The entire exoskeleton, with the linings of the oesophagus, stomach, and intestine, 

 comes off as a whole, 1 and the animal leaves it by drawing the anterior parts of the 

 body backward, and the abdomen and its appendages forward, through an opening 

 made by the elevation of the carapace. When the old carapace falls back into its 



1 The lining of the alimentary tract is of course ruptured. In small lobsters, at the fifth or sixth 

 molt, I have noticed that the break takes place not far behind the stomach-bag, and that while the 

 linings of the masticatory stomach and oesophagus come out by way of the mouth, as in the adult, the 

 lining of the intestine is withdrawn from the anus. 



