30 NATURAL AURANGEMENT OF INSECTS. 



nature of the animal of a barnacle and of a shellfish, 

 as M. Cuvier well observes, is " very different." The 

 Cirrhipedes,in fact, are thetestaceous or shelly Annulosa ; 

 that is, they reprettent the 3Iollusca in the circle of an- 

 nulose animals. Hence the error of M. Cuvier (who so 

 frequently confounded analogy and affinity), in placing 

 thera immediately after the true shellfish, although he 

 justly observes that they have a sort of intermediate 

 station between them and the Articulata ; in other 

 words, they are analogous to the former, and connected 

 with the latter. The body and all the most vital parts 

 of the barnacles are protected by shelly pieces or valves, 

 which fit close to each other, with a single opening at 

 the top, through which the animal protrudes its feet, 

 and imbibes its nourishment ; we say its feet, for such 

 they really are, although they cannot be used as such 

 for locomotion — the animal itself being fixed either by 

 its shell, or by a flexible peduncle immoveable at the 

 base. It was long imagined that the barnacles were 

 produced either from eggs, which were glutinous, and so 

 adhered to the substance on which the full-grown 

 animal was afterwards found, or that they were vivi- 

 parous, the female bringing forth the young alive, and 

 depositing them in suitable situations. Very recently, 

 however, a naturalist of our own country. Dr. Thomp- 

 son, has made known the extraordinary fact, that these 

 creatures undergo a metamorphosis no less surprising 

 than that of perfect insects. This, of cours^ removes 

 all doubts of the true station which the Cirrhipedes oc- 

 cupy in the natural system, and at once places them in 

 the circle of Annulosa, even if the possession of articu- 

 lated limbs were not sufficient to place them strictly 

 within that circle. 



(27.) The anatomical structure of these animals may 

 be thus briefly stated : — The vital parts are enveloped 

 in a mantle or tunic, which is covered externally by shelly 

 plates, varying in number and shape ; thus bearing a 

 strong analogy to the Dithyra, or bivalve shell. That 



