10S balanidjs. 



legs, in the larva in the first stage, are apparently the very 

 same as the first three pairs, in the larva in the second 

 stage, and in the pupa. And in the pupa the first three 

 pairs, which certainly correspond with the first three pairs 

 of cirri in the mature animal, seem to me, for reasons pre- 

 sently to be assigned, to be the second, third, and fourth 

 thoracic limbs. Hence I am led to the conclusion that 

 the first pair of legs in the larva in the first stage, are 

 homologically the second thoracic (answering to the third 

 pair of maxillipeds in the higher Crustaceans), and that the 

 two succeeding pairs are the third and fourth thoracic limbs ; 

 to be succeeded, in the pupal stage, by the fifth, sixth, and 

 seventh thoracic appendages. 



Lastly, behind the natatory legs, on the ventral surface, 

 (PL 29, figs. 8, 9, i), the body is much produced, and ter- 

 minates in a horny fork, which, after the first moult (fig. 10, «), 

 becomes much elongated. Anteriorly to this fork, on the 

 ventral surface, there is another fork (/), and again above 

 this I could distinguish, in Chthamalus stellatus, after the 

 first moult, another fork (m), or at least a pair of short thick 

 spines. From the structure of the forked abdomen in the 

 known larvae of the Podophthalmia, I presume that this 

 portion of the body is the abdomen of the young Cirripede, 

 but it is not at all plainly articulated. After the first moult, 

 the posterior end of the carapace (/*), which is always pointed, 

 becomes much elongated and serrated on both sides ;* re- 

 minding one of the structure of the carapace of the so-called 



Hippolyte varians, and I found, on dissection, the view of M. Joly, that the 

 three pairs of natatory legs are the maxillipeds, so far strongly confirmed, that 

 they followed closely, with equal intervals, the mandibles aud two pairs of 

 maxillae. The first pair of natatory legs in Caradina, in its earliest condition 

 within the egg, is uniramous, like the first pair in the larvse of Cirripedes. 

 There is one fact which seems rather strongly opposed to the view of these 

 three pairs of legs in the larvse of the macrourous Crustaceans being the 

 maxillipeds, which is that Capt. Du Cane ('Annals of Nat. Hist., 1838, vol. ii, 

 pi. 6, and 7) observed only three pairs of limbs in process of formation pos- 

 teriorly to the first three pairs, whereas there should be found, in accordance with 

 M. Joly's view, five pairs, i. e. all five pairs of ambulatory legs. This one fact 

 countenances the view, which I hold on the nature of the legs in the larvae 

 of Cirripedes during their early stages, namely, that they are the second, third, 

 and fourth thoracic limbs, to be succeeded by only three additional pairs. 



* I suspect that the account given by Goodsir ('Edinburgh New Phil. 

 Journal/ 1843) of the posterior points of the carapace and abdomen in the 

 larva of a Balanus, is not quite accurate. 



