18 lepadid^e. 



This enigma was at once explained by an examination of 

 the mouth, which was found to be in a rudimentary con- 

 dition and absolutely closed, so that there would be 

 no use in prey being seized. Underneath this slightly 

 prominent and closed mouth, I found all the masticatory 

 organs of a Cirripede, in an immature condition. The 

 state of the mouth will be at once understood, if we 

 suppose very fluid matter to be poured over the pro- 

 tuberant mouth of a Cirripede, so as to run a little way 

 down, in the shape of internal crests, between the dif- 

 ferent parts, and in the shape of a short, shrivelled, 

 certainly closed tube, a little way ('008 of an inch in 

 L. australis) down the oesophagus. Hence, the larva in 

 in this, its last stage, cannot eat; it may be called a 

 locomotive Pupa;* its whole organisation is apparently 

 adapted for the one great end of finding a proper site for 

 its attachment and final metamorphosis. 



Thorax and Limbs, — The thorax is much compressed, 

 and consists of six segments, corresponding with the six 

 pair of natatory legs ; the anterior segments are much 

 plainer (even the first being distinctly separated by a fold 

 from the mouth), than the posterior segments, which is 

 exactly the reverse of what takes place in the mature 

 Cirripede ; in the latter, the first segment is confounded 

 with the part bearing the mouth. The epimeral elements 

 of the thorax are distinguishable ; the sternal surface is 

 very narrow, and is covered with complicated folds and 

 ridges. The six pair of legs are all close, one behind the 

 other, and all are alike in having a haunch or pedicel of 

 two segments, directed forwards, bearing two arms or 

 rami, each composed of two segments, the outer ramus 



* M. Dujardin has lately ('Comptes Rcndus, 5 Feb. 5, 1850, as cited in 

 'Annals of Nat. History,' vol. v, p. 318,) discovered that the "Hypopi are 

 Acari with eight feet, without either mouth or intestine, and which, being 

 deprived of all means of alimentation, fix themselves at will, so as to undergo 

 a final metamorphosis, and they become Gamasi or Uropodi." Here, then, 

 we have an almost exactly analogous case. M. Dujardin asks — " Ought, 

 therefore, the Hypopi to be called larvae, when, under that denomination, 

 have hitherto been comprised animals capable of nourishing themselves ?" 



