CEMENTING APPARATUS. 135 



greater complexity of the cementing apparatus and of the 

 greater number of the excretory orifices in the Balanidae, com- 

 pared with the Lepadidae, is that the entire surface of the 

 broad basis, which answers to the whole peduncle in the Lepa- 

 didae, is firmly cemented down to the supporting object, in- 

 stead of merely the basal end of the peduncle. The cement 

 issues either in a cellular condition, or more commonly as a 

 fine network, which, at a short distance from the orifices 

 (PI. 28, fig. 4#, z), becomes so fine as to form a sheet or 

 layer : I may here recall the fact, that in the cement pro- 

 ceeding from the disc of the antennae, in some species of 

 Lepas, a similar structure was observed. The cement itself 

 presents the same transparent, brown, laminated, structure- 

 less appearance, and the same chemical reaction, as de- 

 scribed in my former volume. The cement has the capacity 

 of occupying and filling up all inequalities in the supporting 

 surface ; I have seen it, when spread over an encrusting 

 Flustra, present an exact model of every cell ; in the case of 

 Coronula, it seems, as we shall immediately see, to have the 

 power of penetrating into, and even almost blending with 

 the epidermis of the supporting Cetacean. The last-formed 

 cement-glands and cement-ducts present a delicate and 

 transparent appearance, and contain cellular matter; whereas 

 the old cement-glands, and sometimes the old cement-ducts, 

 are filled with brownish cement, not acted on by boiling 

 potash. The foregoing remarks are confined to the sub- 

 family Balaninae, for I have not been able to examine 

 thoroughly the Chthamalinae, and can only affirm, that in 

 Chthamalus and Pachylasma the cement-ducts repeatedly 

 bifurcate and inosculate, in the same manner as in the 

 Balaninae. I will now proceed to describe, in some detail, 

 the cementing apparatus in the several following genera. 



Coronula. — The cementing apparatus is here more simple 

 than in any other genus of the Balaninae, and I have studied 

 it more carefully. The basal membrane of Coronula 

 balcenaris is figured in PL 28, fig. 1 a, and must first be 

 described ; its relation to the shell will hardly be understood 

 without looking at the outline of the folded walls of this 

 species, in PI. 10, fig. 5. The basal membrane closes the 

 central circular hollow, and is continuous with rays (not 



