POWERS OF BURROWING. 341 



reason to believe, from some interesting observations made 

 by Mr. W. Thompson, of Belfast, that some sessile cirri- 

 pedes moult about every fortnight. 



Internal Structure of the Cup. — When the cup is dis- 

 solved in acid, each shelly layer is represented by a rather 

 tough, pale-brown membrane, itself composed of numer- 

 ous fine laminae, which, under a one-eighth of an inch 

 object glass, exhibit generally only the appearance of a 

 mezzotinto drawing; but there often were layers of branch- 

 ing vessels, (like moss-agate,) less than the T^cboth of an 

 inch in diameter, and of a darkish colour ; these vessels 

 are not articulated, but otherwise resemble the same 

 peculiar structure in the valves of the capitulum. The 

 exterior yellow membrane is marked, or rather composed 

 of successive narrow rims, which, in fact, are the lines of 

 termination of the laminae of membrane, which in a cal- 

 cified state form the cup itself. In most parts, both on 

 the borders and under the centre of the cup, but not 

 everywhere, there are imbedded in the yellow membrane, 

 elongated, irregular, top-shaped masses of bright yellow 

 chitine, each furnished with a tubulus, which penetrating 

 the calcareous laminae leads to the corium ; the little aper- 

 tures thus formed, are clearly visible in the layers of mem- 

 brane, left after exposure to acid. In L. Nicobarica, the 

 innermost shelly layer of the cup was punctured, like the 

 surface of the shell in Chthamalus and many other sessile 

 Cirripedes, by the internal orifices of these tubuli. The 

 top-shaped masses often have star-shaped summits ; and 

 they differ in no essential respects from those on the lower 

 part of the peduncle, excepting that they are quite im- 

 bedded in the membrane covering the under surface of the 

 cup, whereas those on the peduncle project freely. I 

 found these top-shaped bodies in the outer membrane of 

 the cups in L. dorsalis, L. cauta, and L. Rhodiopus, which 

 alone I was enabled to dissolve in acid ; and [ mention 

 this fact, as indicating the probable presence of the more 

 important star-headed projections on the lower parts of 

 the peduncle in these same species. The basal calcareous 



