their Food and Digestive Organs, 4 1 3> 



order (Tectibr&,nchia) as the Bulla, we find a curious modi- 

 fication of this structure, accompanied, however, with a total 

 discrepancy in the tastes and propensities of the creature ; 

 and this is a fact which deserves to be remembered in esti- 

 mating the value of inferences, in relation to the habits of 

 animals, drawn from their presumed affinities. The oral organs 

 of Bulla and Aplysia are nearly the same, and there is a 

 resemblance in their complicated digestive apparatus; but, in- 

 stead of three shells, the muscular gizzard of the latter is 

 studded with numerous sharp pyramidal knobs of a semi-car- 

 tilaginous consistence, and of unequal sizes, and which may 

 be rubbed off very easily, for they have no muscles to attach 

 and move them. * When Bohadsch saw this structure for 

 the first time, it seemed to him so anomalous and wonderful, 

 that numerous dissections were required to convince him of 

 its being the natural armature of the organ {De Anim. Mar,, 

 p. 19.) ; and he fell into the erroneous conclusion that it was 

 fitted to triturate the shells on which the animal was presumed 

 to prey. {De Anim, Mar., p. 22.) But the Aplysia is really 

 herbivorous, as is asserted by Pessonel, Cuvier, and others; 

 and, were it necessary, I could add my testimony to this fact, 

 having at one time kept a large specimen of Aplysia depilans 

 for nearly three months in a state of confinement, during 

 which it was fed on jPi\ci only, and these it ate greedily, show- 

 ing some partiality to the dulse (JF\\cus palmatus). The food, 

 previously to its reception in this curious gizzard, has passed 

 tlirough a large membranous crop, in which it probably un- 

 dergoes little change : in the gizzard it is broken down, and 

 in this state enters a third stomach, armed also on its internal 

 surface with hook-like prickles directed forwards, and intended, 

 doubtless, to tease the fibrous mass, that it may be more 

 thoroughly subjected to the dissolving virtue of the gastric 

 juices, and reduced to a homogeneous pulp, previously to its 

 commixture with the bile, which flows into this viscus from 

 two large orifices close to the pylorus, opening between two 

 small membranous prominent crests. (Cuvier, Mem. sur les 

 Mollusq, M., ix. 18.) 



* Pessonel's description of this organ is short, but characteristic: — 

 " The membranes are thick, and are set with twelve stones, or horny 

 pieces, of a bright yellow colour, and as transparent as fine yellow amber, 

 ending in points like a diamond j so that the great side, or basis, is set into 

 the membrane of the gizzard, as a diamond in its socket. Others differ in 

 size, having different figures, that, in acting all together, they may be able 

 to break and grind the herbs the animal feeds upon, as well by the strength 

 of the muscle, or gizzard, which puts them into action, as by the situation 

 of these stones, assisted by grains of sand found in it, turning the whole by 

 this trituration into a liquor." (Phil. Trans., vol. 50., 1758, p. 587.) 



