126 BALANID.E. 



of the mouth of three other segments), have come to ad- 

 here by their dorsal surfaces to the internal surface of the 

 carapace, — that is, of the first three segments, which ought 

 of course to have stood quite in advance of these two seg- 

 ments, and these two segments again ought to have stood 

 in advance of the mouth. The mouth is directed pos- 

 teriorly, instead of from the body ; and the three segments 

 of which it is formed (closed at their anterior end by the 

 labrum), and are very small compared to the relatively mon- 

 strously great, three anterior cephalic segments, composing 

 the carapace. To place the segments of the body of Pro- 

 teolepas in proper sequence, in respect to those of the cara- 

 pace, and in accordance with the sequence of the archetype 

 Crustacean, it would be necessary, by seizing the extremity 

 of the abdomen (a), to tear the two segments succeeding 

 the mouth from their dorsal attachment, as far back as the 

 basal margin of the labrum ; and then pull them till they 

 stood posteriorly to (or in the diagram, above) the mouth ; 

 which latter part would, by the same movement, be made 

 to project out at right angles to the ventral surface, and 

 would then be preceded only by the first three, great, con- 

 fluent segments of the head, which being produced back- 

 wards, form the carapace. All that has just been said on the 

 position, in Proteolepas, of the segments of the body in rela- 

 tion to those forming the carapace, I believe to be applicable 

 to all ordinary Cirripedes, with this difference, that in the 

 latter, after the metamorphosis, the two segments succeed- 

 ing the mouth quite disappear on the ventral surface, and 

 dorsally are either aborted or have coalesced with the ad- 

 joining segments. 



When the due time for the act of metamorphosis has 

 arrived, the pupal carapace splits along the dorsal ridge, and 

 is cast off, together with the acoustic sacks, the basal seg- 

 ments of the two antennae, and the great, black, compound 

 eyes, hanging to the UU-like apodemes. The three terminal 

 segments of the antennas invariably remain cemented to 

 the surface of attachment. The exuviae usually continue 

 for a time united to the cemented antennae, but are finally 

 washed away. Besides the split along the dorsal ridge, the 



