ME. R. GARNER ON THE SHELL-BEARINO MOLLUSCA. 35 



formance of sloughing in a forest of Zostera, on one of the mud 

 banks in Poole Harbour, and while scraping these weeds with a 

 keer-drag it fortunately fell into my net. It shows how the Bra- 

 chyura leave their old shells by the horizontal splitting away of the 

 carapace from the other portions of the shell — the carapace itself 

 remaining entire ; and it also shows (and this was my principal 

 object in exhibiting the specimen) the enormous amount of increase 

 of size upon emerging from the shell, and the rapidity with which 

 that increase takes place. The animal, as now seen, is in exactly 

 the same state as when taken out of the water, and its bulk is 

 probably some four times larger than the area of the shell in which 

 it had been encased only a few minutes before. I retained the 

 Crab in connexion with its old shell, and prevented its further 

 escape by wrapping it in paper, so that it could not move its limbs. 

 I thought such a specimen would be telling and illustrative, and that 

 the old shell, being in contact with the new, would afford facilities 

 for contrast. In this condition the Crab died, and, being out of water 

 some time, it became dry, and the soft new shell collapsed and 

 bulged in ; but, upon placing the dead Crab in sea- water, the soft 

 shell very speedily imbibed sufficient fluid to distend it to its pre- 

 vious dimensions. This of course was simply the effect of endosmosis. 

 Mr. Couch, in describing the moulting of the common Edible Crab 

 (Cancer Pagurus), speaks of its drinking large quantities of water, 

 and thus becoming distended ; but I rather think that the distension 

 takes place by endosmosis, even during life. There are two cir- 

 cumstances which militate against Mr. Couch's opinion : — first, 

 the rapidity with which the distension occurred in the Crab I have 

 just exhibited, while still in the act of moulting ; and secondly, 

 that after death the same distension occurred when the Crab was 

 immersed in sea- water ; in which case it could only be by endosmosis. 

 Indeed to me it seems very probable that this very endosmosis, 

 when the water once comes in contact with the new, uncalcified 

 shell, may, by distending it, be the main agent in the breaking 

 open and dissevering of the elements of the old shell. 



On the Shell-bearing Mollusca, particularly with regard to Struc- 

 ture and Form. By Egbert Gtarner, Esq., F.L.S. 



[Abstract of a Paper read before the Society.] 



The author commences the paper, of which the following is the 

 substance, with some general observations on the morphology of 



3# 



