NEEVOUS SYSTEM OF PENTELASMIS. 



451 



Fig. 233. 



the shell would represent this thorax, which would be divided into five 

 pieces ; the first pair of cirri arising from the body would then repre- 

 sent the true feet of a Crustacean ; the branchiae would occupy the same 

 position in both ; the rest of the body of the Barnacle, namely that 

 which supports the five other pairs of feet, would represent the tail of 

 the Crustacean, and the ciliated, natatory feet, generally connected with 

 that part of the external skeleton. Even the mouth, as the author 

 referred to might have added, with its triple series of jaws, is more 

 nearly allied in structure to that of the Crustaceans than to anything 

 we shall meet with in the structure of the oral organs of true Mollusca. 

 (1166.) But the affinity which unites the Cirrhopoda to the Homo- 

 gangliata is not merely exemplified in the analogies that can be pointed 

 out between the external configuration 

 of Pentelasmis and some Crustacean 

 forms ; the nervous system even, as we 

 might be led to anticipate from the 

 symmetrical arrangement of the articu- 

 lated cirri, still exhibits the Homo- 

 gangliate condition, and, besides the 

 supra-oasophageal masses, forms a lon- 

 gitudinal chain of double ganglia ar- 

 ranged along the ventral surface of the 

 body, from which the nerves supplying 

 the cirriferous arms take their origins. 

 Four small tubercles (fig. 233)*, placed 

 transversely above the oesophagus, re- 

 present the brain, and give origin to 

 four principal nerves (////), which 

 are distributed to the muscles and vis- 

 cera ; for in such a situation, organs of 



Pentelasmis vitrea, exhibiting the ner- 

 TOUS system : a a, the pedicle ; 6 5, the 

 body ; c, the mouth ; A d, glandular 



, ., , n , {, masses ',ff, visceral nerves ; o o, nervous 



SUITOUnd the OeSOphagUS, trom each Ot co u ar surrounding the oesophagus ; A, i, 



Below 



sense would evidently be useless. Two 

 lateral cords, derived from the above, 



k, I, m, series of double ganglia supplying 

 the articulated cirri. (After Cuvier.) 



which a nerve (o o) is given off. 

 the oesophagus the nervous collar ter- 

 minates in a pair of ganglia (h), that give origin to the nerves supplied 

 to the first pair of arms ; and then succeeds a parallel series of double 

 ganglia (i, ~k, I, m), exactly resembling those of articulated animals, 

 from which emanate nerves that are destined to the cirri and surround- 

 ing parts. 



(1167.) The muscular system of Pentelasmis is partly appropriated 

 to the movements of the shell and partly to the general motions of 

 the body. The shell is closed by a single transverse fasciculus of 

 muscular fibres, whereof a section is seen at e, fig. 232, placed imme- 



* Cuvier, loc. cit. 



