BAUNACLES. 71 



have amply confirmed.* Mr. Thompson, in tlic spring of 1 826, 

 took, in a small towing-net, a nimiber of minute translucent 

 creatures about the tenth of an inch in length and of a some- 

 what brownish tint.t They were taken on the first of May, 

 and kept alive in a glass of sea- water. They appeared like 

 small Crustacea. On the nierht of the eisrhth, two of them had 

 thrown ofi' their outer skin, and were firmly attached to the 

 bottom of the vessel, when they rapidly assumed the apparel 

 of the sessile Barnacles or Acorn-shells [Balanus pusillus). 



The pedunculated Barnacles, or those with the long pedicle, 

 present, in their young state, an appearance very dissimilar; 

 but, in all essential particidars, the change from their transitory 

 swimming condition to their pcnnanently adhesive state is 

 precisely similar. In their perfect state {Figs. 42, 43) they 

 are described by Mr. Owen as being "symmetrical animals, 

 with a soft unarticulated body enveloped in a membrane. 

 They are provided with six pair of rudimentary feet, obscurely 

 divided into three joints, and terminated each by a pair of 

 long and slender, many-jointed, ciliated tentacles, curled 

 towards the mouth, and thence giving origin to the name of 

 the class" {Cirripeda, curl-footed). J 



The Acorn-shell is based on a deposit of calcareous matter, 

 and has a shell composed of many pieces, and thus capable 

 of enlargement according to the wants of the animal. It was 

 formerly classed with the Barnacle among the Multival ve shells, 

 the contained animals being regarded as MoUusca, or to use a 

 more common phrase, as "shell-fish." Their structure and 

 their changes being now better understood, they constitute 

 of themselves a small but interesting class, aUied to that of 

 the crustaceous animals, which constitute the next division. 

 The sexes have been ascertained to be distinct. § 



The cheapness of the pleasures which natural history aff'ords 

 should of itself form a reason for the general cultivation of 

 such pursuits. They are within the reach of the most humble, 

 and are not dependent on costly or complicated apparatus. 

 By means so simple as a glass of sea-water, we have caused 

 the Balani or Acorn-shells to exhibit a series of movements, 

 which we have never shown to the youth of either sex without 



• Vide ante, page 46. 



+ Zoological Researches, Memoir iv. page 78, plate xi. 



X Lectures, page 155. 



§ H. D. Goodsir, in Edinburgh Philosophical Journal, July, 1813. 



