METAMORPHOSES OF CIRRIPEDES. 105 



wards ; and within these horns I distinctly saw an articulated 

 organ. These horns are difficult to be distinguished, and 

 probably could not be made out previously to the first moult, 

 in any larva of less size than that of Scalpellum vulgare. 

 But after the first moult, Mr. Bate has seen, in two species 

 of Balanus, in Verruca and in Chthamalus (fig. 10, b), a pair 

 of articulated organs, in this same position, evidently now 

 forming antennae, and directed anteriorly, and free from any 

 envelope. It is somewhat important, as we shall presently 

 see, to bear in mind that these antennae} first appear within 

 an envelope or horn ; and that I detected that they included 

 an articulated organ, before I had heard of Mr. Bate's ob- 

 servations. These antennae, from their small size, from being 

 seated internally with respect to the horns containing the 

 other pair of antennae, and from the position which the latter 

 assume in the later stages of the larva, I believe to be the 

 first or anterior pair. Their position in appearance poste- 

 riorly to the large lateral horns, containing the second pair 

 of antennae, is probably due to the anterior cephalic seg- 

 ments having been driven inwards, the truncated outline 

 of the front of the head, and likewise, probably, the position 

 of the mouth between the bases of the natatory legs being 

 thus caused. 



In this same larva of Scalpellum vulgare, within the great 

 lateral horns just alluded to (fig.8,c), filiform organs, support- 

 ing rows of spines, could be distinguished; and these appeared 

 to me to be antennae. These horns or cases resemble in 

 structure the smaller pair just described ; they arise from 

 the ventral surface, and can hardly, therefore, be considered 

 as prolongations of the carapace. After the first moult 

 (fig. 10, c) they are seen to have increased much in length : 

 in some cases they are of considerable length before the first 

 moult, as in Lepas : in the Balanidae they seem to be gene- 

 rally shorter than in the Lepadidae ; but in Balanus elon- 

 gatus I found them one third of the entire length of the 

 animal. Whilst within the egg, these horns are adpressed 

 laterally to the body, and so point posteriorly ; afterwards 

 they project rectangularly from the sides, or, as in Seal- 

 pellum vulgare, are directed somewhat anteriorly. As in 

 the larvae of all ordinary Crustaceans, as yet known, the an- 



