. . .; these lead, as described in my former volume, into a sack, with a bag suspended in it, which is provided with a large nerve, and which I believe[Pg 114] to be the acoustic vesicle. These orifices occur in the carapace, either in the same position, or a little more posteriorly, in the pupæ of all Cirripedes. In Balanus balanoides they are minute, being only 2/6000th in diameter, but are surrounded with a border: in Conchoderma virgata they are also surrounded by a border: in Lepas pectinata, the orifices are 3/6000th of an inch in diameter, and are very singular from being seated on rounded prominences, causing the carapace to have two short, blunt horns in front. In Lepas australis, and I believe in the other species, the corium round the acoustic orifices is darkly coloured; and these coloured marks can be distinguished for some little time on the peduncle of the young Cirripede, after the metamorphosis, and after the entire organ, together with the whole pupa. . . Read More