IISTACEANS. 117 



in-xt. when the roe is in on early stage, and then by ordinary fishery, 

 when attracted l>y Itait. Of the lirst kind, Olivi computes that 86,000 

 pounds weight are taken ; of the second, 12,320,000 pounds ; and of the 

 tliinl. 'J.'ii'i'i.oOO pounds. The quantity must appear incredible, but the 

 size of the species probably exceeds that of those of Britain. Zoologia 

 . pp. .").;-.").'). Tliis author calculates the gross quantity as worth 

 half a million of Venetian money. 



Olivi speaks likewise of the wonderful number of other species, of 

 which I shall say nothing, being ignorant whether we have any of them 

 in Scotland. 



Some genera are as peaceable, tranquil, and inactive, as others are 

 the reverse. They select the clefts of the rocks, or retreat under stones, 

 which appear to be occupied as a permanent abode until hunger calls them 

 from it. All prefer concealment ; they always desire cover, whence, for 

 smaller specimen*, it is beneficial to introduce the single valve of some 

 large shell into their vessels, under which they will crawl and enjoy 

 a long repose. 



From the inactive habits of several species, many specimens are 

 overgrown with marine vegetables ; their surface serves as a nidus for 

 zoophytes, or numerous shells adhere to it. I have seen the carapace 

 of one totally invested by a sponge ; not a particle free. 



When the profusion of parasites is great, the subjects evidently suffer 

 under it and perhaps they perish. 



Exposed to so many sources of destruction, it is surprising how any 

 remain, but the excessive fecundity of the tribe, in general, contributes 

 to their preservation. 



\\ere the progeny of a single female common crab spared but for 

 two seasons of maturity, their multitude would probably satisfy the de- 

 mands of 10,000 people. 



I am not aware that any of tin- Crustaceans are androgynous, though 

 perhaps credited formerly. In many, especially among the Decapodes, the 

 difference of two sexes is well defined, and in some it may be recognized, by 



-imple rules, from the formation of the shell. The breast-plate, thorax, 

 or apron of the female of the common cn\l>, is a brood triangular portion 



