36 LEPADID.E. 



each giving out cement-ducts, which, bifurcating in the 

 most complicated manner, pass outside the shell and thus 

 attach it to some foreign body. 



The cement, removed from the outside of a Cirripede, 

 consists of a thin layer of very tough, bright-brown, 

 transparent, laminated substance, exhibiting no structure 

 under the highest powers, or at most a very fine dotted 

 appearance, like a mezzotinto drawing. It is of the 

 nature of chitine ; but boiling caustic potash has rather 

 more effect on it than on true chitine ; and I think 

 boiling nitric acid rather less effect. In one single 

 instance, namely, in Coronula, the cement conies out of 

 the four orifices of the two bifurcating ducts, in the 

 shape of distinct cells, which, between the whale's skin 

 and the basal membrane, arrange themselves so as to 

 make a circular, continuous slip of cement; then the 

 cells blend together, and are converted into transparent, 

 structureless cement. Cementing tissue or membrane 

 would, perhaps, have been a more correct title than 

 cement ; but, in ordinary cases, its appearance is so little 

 like that of an organised tissue, that I have for this 

 reason, and for brevity-sake, preferred the simple term of 

 Cement. 



In the larva the cement always escapes through the pre- 

 hensile antennae ; and it thus continues to do throughout 

 life in most or all of the species of Lepas, Conchoderma, 

 Dichelaspis and Ibla. In the first two of these genera, 

 the cement escapes from the borders of the lower side of 

 the disc or penultimate segment of the antennae, and can 

 be there seen radiating out like spokes, which at their 

 ends divide into finer and finer branches, till a uniform 

 sheet of cement is formed, fastening the antennas and 

 the adjoining part of the peduncle down to the surface of 

 attachment. In Dichelaspis Warwickii and Scalpellnm 

 Peronii, the cement, or part at least, comes out of the 

 ultimate segment of the antennae, in the shape of one tube, 

 within another tube of considerable diameter and length. 

 In Scalpelhm vulgar e, and probably in some of the other 



