518 verrucidjE. 



of basal membrane becomes, after a new rim has been 

 formed and as the shell grows outwards, firmly cemented 

 down to the now slightly excavated surface of attachment ; 

 but during all the time the solvent goes on acting in the 

 middle, and continues, during the whole growth of the shell, 

 to encroach on and dissolve the supporting surface from 

 under the inner edges of the previously cemented down, 

 circular zone of basal membrane. I have discussed this 

 subject at considerable length, as it appears to me an 

 interesting one. In this case we have the action of cilise* 

 and of respiratory currents, to which in the case of Mollusca 

 so much has been attributed, entirely eliminated. It is, 

 also, an interesting fact, that within the same Order we 

 should have some Cirripedes boring by simply mechanical 

 means, and others by a chemical solvent.f 



1. Verruca Stromia. PL 21, fig. 1 a — If. 



Lepas Stromia. 0. Miiller. Zoolog. Dan. Prod., No. 3025, 1776. 



— — lb. Zoolog. Dan., vol. 3, Tab. 94, 1789. 



— striata. Tennant. British Zoology, vol. 4, Tab. 38, fig. 7, 



1777. 

 Die warzenformige meereichel. Spcngler. Schriften der Berlin. 



Gcsell., 1 B., Tab. 5, fig. 1—3, 1780. 

 Lepas verruca. Spengler. Skrifter af Naturhist. Selskabet, 1 B., 



1790. 



— — et Stromia. Gmelln. Syst. Nat., 1789. 

 Balanus veruca. Bruguicre. Encyclop. Meth., 1789; Clisia verru- 

 cosa , Deshaycs, in Tab. 



— intertextus. Tulteney. Catalogue of Shells of Dorset- 



shire, 1799. 

 Lepas striatus. Montagu. Test. Brit., 1803. 



— verruca. Wood's General Conchology, PI. 9, fig. 5,1815. 

 Verruca Stromii. Schumacher. Essai d'un Nouveau Syst. Class., 



1817. 

 Creusia Stromia et verruca. Lamarck. Animaux sans Ver- 



tebres, 1818. 



* See the previous note to p. 516. 



f The solvent may be carbonic acid gas, as suggested by Mr. C. S. Bate in 

 the case of Mollusca ('Report of British Association,' 1849, p. 73), but here, 

 under the basal membrane, we cannot have the respiratory currents, or the 

 ciliary action (see note, supra), as likewise suggested by Mr. Bate. 



