116 balanim;. 



pairs, also attached to their bases, but directed dorso-pos- 

 teriorly, so that altogether there are five pairs of muscles 

 attached to the apodemes ; their chief function, I should 

 think, was to draw the antennas posteriorly and upwards 

 within the carapace ; but as the apodemes cannot be moved 

 without the great compound eyes being likewise moved, 

 the muscles probably serve a double purpose. When the 

 pupae were alive, I noticed that their eyes were constantly 

 kept in a state of vibratory movement. Flexor and ex- 

 tensor muscles are attached at one end to the posterior 

 margin of the basal segment, and at the other end to the 

 second or main segment ; other powerful muscles attached 

 to this latter segment, are prolonged by ligaments into the 

 disc. In Cryptophialus I observed that the disc-segment 

 had a movement almost like that of the wrist. Whether 

 any muscles enter the small terminal segment, I know not. 

 The drawing in PL 30, fig. 8, of part of the second segment, 

 of the third or disc segment, and of the fourth or ultimate 

 segment, in Lepas australis, is, I think, very accurate. The 

 second segment articulates on the upper or dorsal surface 

 of the disc, and has the articulation on one side constricted 

 and formed of thin and flexible membrane ; the little ter- 

 minal segment, which is turned outwards at right angles, 

 also, articulates on the disc. That the disc forms a true 

 segment is shown clearly in Cryptophialus (PL 24, fig. 18), 

 where the articulation with the second segment is not in 

 such close contact. The disc is either circular, as in Lepas, 

 or hoof-shaped, as in Ibla : in B. balanoides the disc is 

 rather hollowed out on the inner side. It has the power 

 of adhering even to so smooth a substance as glass, placed 

 vertically. It is surrounded by a rim of transparent mem- 

 brane. On the hinder margin some spines arise from the 

 central and mure opaque part : in Lepas austral is, there are 

 no less than seven of these spines (fig. 8) : in Conchoderma 

 virgata there are only four, in Scaljjellum and Ibla only 

 one. When the disc is placed on the surface of attachment, 

 these spines lie parallel to it. The middle part of the disc 

 is, almost always, nearly opaque ; and in tracing the cement- 

 ducts from within the body of the pupa, or of the young 

 Cirripede, I in many cases traced them as far as this 



