CIRRHOPODA ; BALANUS, ETC. 285 



within the shell. The growth of this shelly box is provided for 

 by additions to the edges of the several plates of which it is 

 composed ; these additions increasing the size of the whole, 

 without altering its form. Between the internal and external 

 layers of each valve, there is a regular cancellated or minutely- 

 chambered structure, like that of Bone (Airai. PHYSIOL. 47) ; 

 and this appears to be filled, as in it, with a sort of marrow. No 

 structure resembling this has been found in any Mollusca. The 

 Balanidae are generally found attached by their bases to rocks, 

 wood, shells, Crustacea, and similar marine objects. Those 

 which attach themselves to soft, living objects, appear to become 

 gradually imbedded in them, but rather by the increase of the 

 body to which they are affixed, than by any burrowing power of 

 their own. Thus the Acastce are generally found imbedded in 

 sponges, and one species in the fleshy cortical substance of the 

 Isis, a kind of Polype ; whilst the Coronulce and some members 

 of allied genera, which are parasitic upon Whales, are always 

 found to be more or less covered by the epidermis of their hosts, 

 and in some cases processes of this are actually formed in the 

 chambers of the shell. 



898. The other two sections of the Order may be dismissed 

 in few words, as, although highly interesting to the philosophical 

 zoologist, it would be impossible to give the general reader any 

 idea of their remarkable peculiarities of structure within th- 

 limits to which we are necessarily confined. The section AB 

 DOMINALIA includes only the single species Cryptophialus minu- 

 tus t remarkable as being the smallest known species of Cirrho- 

 pod, and also from its living in vast numbers in small holes 

 drilled in the shells of living specimens of another Cirrhopod, the 

 Concholepas peruviana, amongst the Chonos Islands, off the coast 

 of Chili. It is also remarkable from its having the sexes sepa- 

 rate ; the males being minute creatures, protected within the 

 chamber of the females, to which they adhere by their antennas. 

 The section APODA also includes only a single species, but 

 this is still more singular in its characters than that just referred 

 to. The Proteolepas bivincta rather resembles a spindle-shaped 

 worm, or the larva of an insect, than a Cirrhopod ; it consists of 



