METAMORPHOSES OF CIRRIPEDES. 125 



position of the body of the young Cirripede within the body 

 of the pupa, the alimentary canal becomes shortened to fully 

 half its former length. At the same time, the interspace 

 between the mouth and first pair of legs of the pupa, (con- 

 sisting of the seventh and eighth segments of the archetype), 

 is quite lost in the Cirripede by coalescence. The final cause 

 of the thorax of the young Cirripede not being developed 

 within the thorax of the pupa, probably is, that the cirri 

 may be formed of considerable length, so as to be imme- 

 diately enabled to seize prey ; and that the thorax, which 

 supports the cirri (and this probably is even more important) 

 should be as free as possible within the sack, so as to aid 

 the captorial action of the cirri. 



After these remarks, more especially with regard to the 

 formation of the sack, if any one will look at the sectional 

 drawing of a pedunculated Cirripede in my former volume, 

 or of a sessile Cirripede (PL 25, fig. 1) in this present volume, 

 in which latter the shell adds to the complexity, he will per- 

 ceive the cause of the extreme difficulty in understanding the 

 relative position of the parts throughout the whole class. 

 Even after I had discovered that the prehensile antennae of 

 the pupa might always be found in the centre of the basis 

 or surface of attachment, and which fact, it might have been 

 thought, should have convinced me that this was the ante- 

 rior end of the whole animal, yet still I fancied that the 

 prominent mouth represented the entire head, and that 

 the shell was something quite distinct. It is clear that 

 others have been equally perplexed ; for that which is the 

 anterior end in the eyes of one naturalist, is the posterior 

 end in the eyes of another ; so with the dorsal and ventral 

 surfaces : one naturalist considers the peduncle of the Lepas 

 as the abdomen ; another considers it as a pair of metamor- 

 phosed, thoracic limbs, &c. ! The probable position of the 

 segments of the body of a mature Cirripede, in relation to 

 the three anterior cephalic segments, or carapace, is shown 

 in the diagram (PL 25, fig. 6) of the supposed position of the 

 mature Proteolepas within its pupal envelopes. Here, in 

 the diagram, the two segments immediately succeeding the 

 mouth (c), which are the # seventh and eighth of the archetype, 

 (for the mouth consists of three segments, and all in front 



