124 balanim:. 



cirri of the Cirripede are formed within the twenty-four ex- 

 tremities of the six pairs of biramous, natatory legs of the 

 pupa. Consequently, in the Cirripede and pupa, thus far, 

 part corresponds with part, notwithstanding that new eyes 

 are formed posteriorly to the old eyes, and new acoustic 

 organs in a quite different position from the old ones ; but 

 now we come to a most important diversity in the meta- 

 morphosis, or rather to follow Professor Owen,* in the me- 

 tagenesis, of the young Cirripede. Although, as just stated, 

 the extremities of the cirri are formed within the legs of the 

 pupa, yet, from the great length of the cirri, they occupy more 

 than the whole of the thorax of the pupa ; so that the thorax 

 of the young Cirripede is not formed within the pre-existing 

 thorax of the pupa, but within that part of the pupa, (homolo- 

 gically a portion of the first three cephalic segments), which 

 lies anteriorly to the thorax. As a consequence of this, the 

 pedicels and lower portions of the cirri, the segments of the 

 thorax and its dorsal surface, all come to occupy a position 

 at nearly right angles to that of the corresponding parts in 

 the pupa : this is shown in PL 30, fig. 2. And as a further 

 consequence, (and this is the more important point), the 

 sack, which both in the young Cirripede and pupa is 

 formed by the overhanging and produced portion of the 

 carapace, and which is internally lined by a reduplication of 

 the membrane of the thorax, is necessarily, owing to the 

 changed position of the thorax, altered in extent and carried 

 much further ; namely, from extending merely parallel to 

 the longitudinal axis of the pupa (from b to b'), it is now in 

 the young Cirripede, in addition, carried (to s) almost quite 

 across the inside of the animal. Hence it comes that the 

 young Cirripede is, as I have said in my former volume, 

 internally almost intersected ; and its body remains attached 

 only by a small space, (see the broken line, round a and b 

 in PL 25, fig. 1, of a Balanus with the shell, &c, removed 

 from one side), to the sternal or ventral, inner surface of the 

 carapace, — the carapace being modified either into the capi- 

 tulum and peduncle, or into the shell with its operculum 

 and basis. As a still further consequence of this change of 



* ' Parthenogenesis,' pp. ]3 and 26. 



