356 CIRRHOPODA. 



ventral surface of the body, from which the nerves supplying the cir- 

 rhiferous arms take their origins. Four small tubercles (jig. 168),* 

 placed transversely above the oesophagus, represent the brain, and 

 give origin to four principal nerves (/?/,//), which are distribut- 

 ed to the muscles and viscera, for in such a situation organs of sense 

 would evidently be useless. Two lateral cords, derived from the 

 above, surround the oesophagus, from each of which a nerve (o, o) 

 is given off. Below the oesophagus the nervous collar terminates 

 in a pair of ganglia (A), that gives origin to the nerves supplied to 

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

 ganglia (i, A:,*/, m), exactly resembling those of articulated animals, 

 from which nerves emanate that are destined to the cirrhi and sur- 

 rounding parts. 



(392.) The muscular system of Pentalasmis is partly appropriat- 

 ed 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,j#g\ 167, placed 

 immediately beneath that fissure in the mantle through which the 

 arms are protruded ; it passes directly across from one valve to the 

 other, and approximates them by its contraction. 



A large muscle, whose origin is seen 'm jig. 167, f, arises from 

 the interior of the mantle, and, as its fibres diverge, spreads over 

 the entire mass of the viscera ; this will evidently draw the body 

 forward, and cause the protrusion of the tentacula, while various 

 muscular slips derived from it scarcely need further description, 

 being destined to move the numerous arms with their jointed 

 cirrhi and the fleshy tubular prolongation (jig' 169, A:) already 

 noticed. 



(393.) The food devoured by the Cirrhopoda would seem to con- 

 sist of various minute animals, such as small Mollusks and micros- 

 copic Crustacea, caught in the water around them by a mechanism at 

 once simple and elegant. Any one who watches the movements of 

 a living Cirrhopod will perceive that its arms, with their appended 

 cirrhi, are in perpetual movement, being alternately thrown out and 

 retracted with great rapidity ; and that, when fully expanded, the 

 plumose and flexible stems form an exquisitely beautiful apparatus, 

 admirably adapted to entangle any nutritious molecules, or minute 

 living creatures, that may happen to be present in the circum- 

 scribed space over which this singular casting-net is thrown, and 



* Cuvier, Ice. cit. 



