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XX. Discovery of the Metamorphosis in the second type of the Cirripedes, viz. the 



Lepades, completing the Natural History of these singular Animals, and con- 



Jlrming their affinity with the Crustacea. By J. V. Thompson, F.L.S, Deputy 



Inspector-General of Hospitals. Communicated hy Sir James Macgrigor, Bart. 



M.D. F.R.S. 



Received January 3, — Read March 5, 1835. 



The Fourth Memoir, published in my Zoological Researches and Illustrations, 

 No. III. page 69, &c., having first made known the real nature of the Cirripedes, the 

 key of which remained concealed in their metamorphosis, it might have been expected 

 that some naturalist favourably situated to investigate the oceanic tribe of these 

 animals, would have been the first to make the same discovery in regard to these, and 

 thereby complete their natural history. It was scarcely to be expected that the 

 honour of this discovery also should be reserved for the author, fixed to one spot, 

 where none of them naturally exist, and are but casually thrown upon our shores by 

 the waves of the Atlantic, attached to pieces of wreck, or brought into port fixed to 

 the bottoms of ships returning from distant voyages. Fortunately, however, two 

 ships of this description came into this harbour (Cork), one from the Mediterranean, 

 the other from North America, which, not being sheathed with copper, had their bot- 

 toms literally covered with Barnacles of the three genera of Lepas, Cineras, and Otion ; 

 and having persons employed expressly for the purpose, numbers of these were brought 

 alive in sea water, amongst which were many with the ova in various stages of their 

 progress, and some ready to hatch, which they eventually did in prodigious numbers, 

 so as to enable him to add the proof of their being, like the Balani, natatory Crusta- 

 cea in their first stage, but of a totally different facies and structure ; a circumstance 

 which determines the propriety of the separation of the Cirripedes into two tribes, 

 and evinces the sagacity of Mr. MacLeay in being the first to indicate that these two 

 tribes, the Balani and Lepades, were not so closely related as generally supposed *. 



The larvae of the Balani, described in Memoir IV. under the external appearance 

 of the bivalve MonocuU {Astracoda), have a pair of pedunculated eyes, more numerous 

 and more completely developed members, approximating to those of Cyclops, and of 

 the perfect Triton ; while, in the present type, or Lepades, the larva resembles some- 

 what that of the Cyclops, which Muller, mistaking for a perfect animal, named Amy- 

 mone, and which can be shown to be common to a great many of the Entomostraca ; 



* See Horae Entomologicae. 



