PICTURESQUE SKETCHES 



of Mollusca a division of the animal kingdom readily 

 distinguished from those which we have already had 

 occasion to refer to, by the possession of a much more 

 distinct nervous centre, and conducting the naturalist 

 by slow and successive steps to that more complicated 

 structure met with in the vertebrated animals, of which 

 the fishes form the least highly organized group. 



The Mollusca, as at present understood, are divided 

 into six classes : some, as the Barnacles (Cmimo- 

 PODA *), fix themselves when young to the surface 

 of various sub-marine bodies, and having no organs 

 connected with the higher senses, and being unable to 

 change their position, are content to cast out at in- 

 tervals their ciliated (or hair-like) arms, which form 

 a net of Nature's own contrivance, and entrap such 

 passing prey as suits their appetite. Others, equally 

 incapable of locomotion, but furnished with arms of 

 different construction, catch their food by similar 

 efforts : these are called BRACHIOPODA.")* The Tu- 

 NICATA,J inclosed in tough leathery bags, are firmly 

 rooted to the rocks, or, collected into singular com- 

 pound masses, float about at the mercy of the waves. 

 The CONCHIFERA inhabit bivalve shells ; the PTERO- 

 PODA || swim in myriads through the sea supported on 

 two fleshy fins, and some of them inclosed in delicate 

 fragile shells; while the GASTEROPODA,H defended in 

 most cases by a shelly covering, creep upon a broad 



* KippoQ (cirrkos), a curled lock of hair ; Troda (poda), feet. 



f* "Bpa^iwv (hrachion), an arm ; Troda (poda), feet. 



J Tunicatus, clad in a tunic or inclosing membrane. 



Concha^ a shell ; fero^ to carry. 



|| Hrepov (pteron), a wing ; iro^a (poda), feet. 



"U YaffTrjp (gaster), the belly ; Troda (poda), feet. 



