METAMORPHOSES OF CIRRIPEDES. 115 



segments of the antennae. The second or main segment 

 (formerly called by me the basal segment) has in some 

 species an upper portion of the membrane of which it 

 is composed, next to the body, excessively thin, and 

 separated from the rest of the membrane composing the 

 segment, by an oblique line (fig. 8, 0), which I mistook for 

 its articulation with the body.* We then come to the 

 disc or third segment ; and lastly to the fourth, or ultimate 

 segment. This ultimate segment, generally, has its external 

 corner projecting up, as a step ; and this sometimes, as in 

 Dichelaspis Warwicftii, gives the appearance of its con- 

 sisting of two segments ; but a careful examination of this 

 part in Ibla, in which the step-like structure is carried to 

 an extreme, makes me believe that there is only one 

 segment. t The prehensile antennae, therefore, like the 

 natatory legs, are formed of four consecutive segments, of 

 which the basal segments give rise to the singular apodemes, 

 presently to be noticed (fig. 7), that carry the great com- 

 pound eyes. This basal segment, in all Cirripedes, is 

 moulted with the eyes, the three other segments invariably 

 remaining cemented to the surface of attachment. 



In the Southern Atlantic I took some specimens of the 

 pupa of Lepas australis, not yet attached, and therefore 

 with the muscles of the antennae, not having suffered any of 

 that absorption, which they undergo, as soon as the pupa is 

 permanently cemented to some floating object. In my 

 former volume I noticed a pair of strong muscles, attached 

 to the tips of the middle forks (PI. 30, fig. 7) of the apodemes, 

 and I now find two pairs attached to the bases of the two 

 outer forks, and directed dorso-anteriorly; and two other 



of Lepas, probably L. australis. I believe this author was the first who made 

 out the structure of the abdomen of the pupa. 



* In the table of measurements of the antennae of the several genera and 

 species of the Lepadidse (p. 286) of my former volume, the articulation, called 

 by me basal, I now know to be really the articulation between the basal and 

 second segment. In the fourth column, headed " Length from end of the disc 

 to the inner margin of the basal articulation," the term inner margin really applies 

 to the oblique curved line separating the thin and scarcely visible membrane 

 from the thicker membrane of that segment. These corrections do not in the 

 least affect the object for which the table was given. 



f In a sketch, sent me by Mr. Dana, of this organ in the pupa of a Lepas 

 from the Antarctic Ocean, I observe that he divides my ultimate segment 

 into two segments. 



