198 



HARDWICKE'S S CI B N CE- GO SS IP. 



correspondeacCj on such phenomena as may come 

 under my own notice and that of my friends, con- 

 nected with the growth and economy of our British 

 Marine Alsfe. 



A CHAPTER ON BARNACLES. 



rpHE common Barnacle {Lepas anatifera, or 

 -*- perhaps Hillii), the soft part of which has so 

 often been mistaken for a little bird, giving rise to 

 tliC strange stories we have been considering, was 

 long a puzzle to zoologists, who differed very much 

 as to its exact place in the animal kingdom. Lin- 

 naeus considered it a nmltivalve mollusk ; but after a 

 great many changes of position Mr. Thompson fully 

 established its claim to be classed with the Crustacea, 

 a sub-class of which, tbe Cirripedia, embraces all 

 the known Barnacles, widely differing as they do in 

 external appearance. The sub-class Cirripedia is 

 divided into three families, — the Lepadidse, or 

 pedunculated Cirripedes; the Verrucidse, or Verrucas, 

 containing only a single genus ; and the Balanidee, 

 or sessile Cirripedes. In the first stages of their 



Fig. 1 19. Larva of Lepas aaJralU, in laststag-e of develnp- 

 ment, greatly enlarged, from Darwin's monograph of tiie 

 Ciri-ipedia : «, antennte with sucking disks ; b, carapace; r, 

 natatory legs; n, apodemes supporting eyes. 



separate existence, the larvse of the whole of this 

 group are free-swimming and furnished with 

 pedunculated eyes. In its last or third stage of 

 development (fig. 119), the larva is covered with a 

 shell or carapace {b), and furnished with six pairs 

 of natatory legs {c) ; also a pair of antennae {a), on 

 each of which is placed a sucking disk, by means 

 of which the pupa attaches itself; there are also 

 two large compound eyes («). The final change is 

 thus described by Mr. Darwin. The pupa attaches 

 itielf to the ohject w-hich is to form its home by 

 means of the two disks, it then moults the shell or 

 carapace, together with the eyes, next the integu. 

 meuts of the thorax and the swimming-iegs ; the 

 antennae are not moulted, but left cemented to the 

 surface of attachment, their muscles converted 



into sinewy fibres ; the corium after a short time is 

 absorbed, and they are then preserved in a func- 

 tionless condition at the base of the peduncle ; the 

 young cirripede assuming its natural position, as 

 shown at fig. 120. The wliole transformation is 



Fig. 120. Young Cirripide (enlarged), immediately after 

 moulting the pupal carapace and assuming its natural posi- 

 tion : a, antennae ; c, natatory legs (not yet moulted, but 

 functionless) ; n, the peduncles. From Darwin. 



very curious, and can best be explained by reference 

 to the accompanying figures, 119 and 120, copied 

 from Darwin's monograph of the Cirripedia. Erom 

 the specimens figured it will be seen what a vast 

 difference there may be in the external appearance 

 of the different individuals of a group of animals 

 between which there exists the closest homological 

 agreement. 



Fig. 121. Lepas anatifera. 



The species of pedunculated Cirriped best 

 kno'^n on our coast is the Lepas anatifera, 



