140 BALANID.E 



much as '004 or 005 of an inch in thickness. It is, how- 

 ever, difficult to ascertain its thickness, from the singular 

 manner in which it penetrates into and almost blends with 

 the epidermis of the whale's skin ; so much so, that for a 

 considerable time I thought (not then knowing anything 

 about the cement of Cirripedes) that this transparent horny 

 substance probably answered to a corn on the human foot 

 produced by pressure. But I soon observed that this horny 

 substance certainly extended into and up the cement-ducts ; 

 and this fact first led me to the examination of the whole 

 subject in the several genera of Lepadidae and Balanidae. 

 It was not difficult to remove the cement-ducts, leaving 

 small portions of the contained cement projecting freely up 

 as points from the general surface of cement. The cement 

 adheres slightly to the whole basal membrane, but chiefly 

 to the yellowish rims or edges of the successive slips • and 

 it is indeed this adhesion which, I believe, produces the 

 rims ; for the circumferential slip, when first split, had very 

 thin ragged edges. The cement also extends under the 

 spoke-like prolongations of the circumferential slip, and 

 likewise some way up the sides of the walls. 



The cement-glands, the trunk, and the ducts, except 

 the two, three, or even four last-formed ones, are all filled 

 with an apparently solid thread of transparent, brownish 

 cement, differing in no respect from the cement under the 

 central parts of the basal membrane. In one instance, in 

 which the last-formed pair of glands and ducts had appa- 

 rently been only just developed, they were so perfectly 

 transparent that I could distinguish them only under certain 

 lights, and I could not perceive any contents. The last- 

 formed glands and ducts always appear very delicate, and 

 include a tube of very delicate tissue, containing more or 

 less of granular matter. The next succeeding pair of glands 

 and ducts are always more opaque, and contain much more 

 granular matter; which, in the next, or next but one, may 

 be seen passing into the state of pale brown, transparent 

 chitine. I have seen some most distinct instances, in which, 

 in the same duct, the part towards the centre of the basis was 

 filled with homogeneous cement, and the part towards the 

 circumference with still plainly granular matter. In the 



