METAMORPHOSES. 23 



whole thorax of the larva; no part whatever of the 

 thorax of the Cirripede is formed within the thorax 

 of the larva, but (together with the pedicels of the an- 

 terior cirri) within the cephalic cavity. As a consequence 

 of this, the longitudinal axis of the thorax of the young 

 Cirripede lies almost transversely to the longitudinal axis 

 of the larva ; and the Cirripede, from this transverse 

 position of its thorax, comes to be, as it were, internally, 

 almost cut in twain, and the sack thus produced. As 

 soon as the young Cirripede is free and can move itself, 

 the cirri are curled up, and the thorax is advanced to- 

 wards the orifice of the capitulum, its longitudinal axis 

 resuming the position of approximate parallelism to the 

 longitudinal axis of the whole body, which it had in the 

 larval condition. The reader will, perhaps, understand 

 what I mean, if he will look at the mature Cirripede, 

 figured in PL IX, fig. 4. In this, he will see that the 

 body or thorax is united to the peduncle only by a small 

 part below the mouth ; on the other hand, if he imagines 

 the whole bottom of the body (as high up as the letter It) 

 united and blended into the peduncle, he will see the 

 state in which these parts exist in the larva. Now, let him 

 greatly shorten the cirri, so as to resemble the natatory 

 legs of the larva, and then imagine a young Cirripede, 

 with cirri of full length, formed within the old one, he 

 will see that the new thorax supporting the cirri will 

 have to be developed in an almost transverse position, — 

 the animal consequently being internally almost separated 

 into twain. 



Of the internal organs, whilst the Cirripede is still 

 within the larva, I have already mentioned the stomach 

 with its pair of caeca : from the retracted position of the 

 thorax and rudimentary abdomen, and consequently of 

 the anus, compared with these parts in the larva, the 

 alimentary canal is not above half its former length. 

 There is, as yet, no trace of the filaments supposed by 

 some to act as branchiae, at the base of the first pair 

 of cirri. Nor could I perceive a trace of the testes or 



