452 CIEEHOPODA. 



diately 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. 



(1168.) A large muscle, whose origin is seen in fig. 232, /, 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 for- 

 ward 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 cirri and the fleshy 

 tubular prolongation (fig. 235, &) already noticed. 



(1169.) The food devoured by the Cirrhopoda would seem to consist 

 of various minute animals, such as small Mollusks and microscopic 

 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 cirri, 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 circumscribed space over which this singular 

 casting-net is thrown, and drag them down into the vicinity of the 

 mouth, where, being seized by the jaws, they are crushed and prepared 

 for digestion. No sense but that of touch is required for the success of 

 this singular mode of fishing ; and the delicacy with which the tentacula 

 perceive the slightest contact of a foreign body shows that they are 

 eminently sensible to tactile impressions. As regards the digestive 

 organs, we have already described the prominent mouth (fig. 235, 6), 

 with its horny palpiferous lip and three pairs of lateral jaws. The 

 O3sophagus (c) is short, and firm in its texture ; it receives the excretory 

 ducts of two salivary glands of considerable size (fig. 233, d d), and 

 soon terminates in a capacious stomachal receptacle, the walls of which 

 are deeply sacculated and surrounded by a mass of glandular caeca 

 (fig. 235, d} that represent the liver, and pour their secretion through 

 numerous wide apertures into the cavity of the stomach itself. The 

 intestine (0, /) is a simple tube, and runs along the dorsal aspect of 

 the animal, wide at its commencement, but gradually tapering towards 

 its anal extremity ; it terminates at the root of the tubular prolonga- 

 tion (fc) by a narrow orifice, into which a small bristle (g) has been 

 inserted. 



(1170.) Little is satisfactorily known relative to the arrangement of 

 the blood-vessels and the course of the circulation in these animals. Poli 

 imagined that he had discovered a contractile dorsal vessel, intimating 

 that he had perceived its pulsations in the vicinity of the anal extremity 

 of the body ; and although his observations upon this subject have not 

 been confirmed by subsequent investigations, analogy would lead us to 



