SCALPELLUM. 13 



I may further state, that in the several Orders of Cirripedia such important differences 

 of structure are presented, that there is scarcely more than one great character by which all 

 Cirripedia may be distinguished from other Crustacea : this character is, that they are 

 attached to some foreign object by a tissue or secretion (for at present I hardly know which 

 to call it), which debouches, in the first instance, through the prehensile antennae of the 

 larva, the antennae being thus embedded and preserved in the centre of the basis. The 

 cementing substance is brought to its point of debouchement by a duct, leading from a 

 gland, which (and this is perhaps the most remarkable point in the natural history of the 

 Class) is part of and continuous with the branching ovaria. When we look at a Cirripede, we, 

 in fact, see only a Crustacean, with the first three segments of its head much developed and 

 enclosing the rest of the body, and with the anterior end of this metamorphosed head fixed 

 by a most peculiar substance, homologically connected with the generative system, to a rock 

 or other surface of attachment. 



Genus — Scalpellum. 



ScALPELLUM. Leach. Journ. de Physique, t. Ixxxv, July, 1817. 



Lepas. Linn. Systema Naturae, 17G7. 



PoLLlciPES. Lamarck. Animaux sans Vertebres. 



PoLYLEPAS. De Blalnville. Diet, des Sc. Nat,, 1824. 



Smilium (pars generis). Leach. Zoolog. Journal, Vol. 2, July, 1825. 



Calantica (pars generis). J. E. Graij. Annals of Philosophy, vol. x, (2d series,) 



Aug. 182.5. 

 Thaliella (pars generis). J. E. Gray. Proc. Zoolog. Soc, 1848. 

 Anatifa. Quoij et Gaimard, Voyage de 1' Astrolabe, 182G — 34. 

 XiPiiiDiUM (pars generis). JDixon. Geology of Suffolk, 1850. 



Valvis 12 ad 15: Laterihus verticelli inferioris quatuor vol sex, lineis incrementi 

 plerumque convergentihus ; Subrostrum rarissime adest : Pedunculo squamifero, rarissime 

 nudo. 



suspect to be auditory organs ; this part, therefore, I think, must unquestionably consist of the first two or 

 three segments of the head : within it, even before the larva moults, the incipient striaeless muscles and 

 ovaria of the peduncle can be distinctly traced : immediately after the moult, we see this anterior part 

 converted into a perfect peduncle ; and for some time afterwards certain coloured marks, indicating the 

 former position of the (so called) olfactory cavities and of the cast-oif compound eyes, are still preserved. 

 The prehensile antennae are not cast off, for they are fastened down by the cementing substance, and are 

 thus preserved in a functionless condition, with their muscles absorbed; after a time even the corium is 

 ■withdrawn from within them. From the above and other coloured marks, and from the antennaj being 

 preserved, it is easy to point out, in the peduncle of a young though perfect Lepas, the exact point which 

 each part occupied in the head of the natatory larva. 



Since the above was written, I find that Loven has taken the same view of the homologies of the 

 external parts of the Cirripedia ; in his description of his Alepas squalicola, (Ofversigtof Kongl. Vetens., &c., 

 Stockholm, 1844, pp. 192 — 4,) he uses the following words : " Capitis reliquse partes, utin Lepadibus semper, 

 in pedunculum mutalce et involucrum,'" &c, ; his involucrum is the same as the Capitulum of this work. 



