312 ZOOPHAGOUS MOLLUSCA. 



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, and he fell 

 into the erroneous conclusion that it was fitted to tritu- 

 rate the shells on which the animal was presumed to prey, f 

 But the Aplysia is really herbivorous, as is asserted by Pes- 

 sonel, Cuvier, and others ; j; and, were it necessary, I could 

 add my testimony to this fact, having at one time kept a 

 large specimen of Aplysia mustelina for nearly three months 

 in a state of confinement, during which it was fed on fuci 

 only, and these it ate greedily, showing some partiality to 

 the Dulse (Fucus palmatus). The food, previously to its 

 reception in this curious gizzard, has passed through a large 

 membranous crojj, in which it probably undergoes 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. § 



Among the other families of Gasteropods, 1 do not 

 remember any that are exclusively carnivorous, except the 

 genus Testacellus, to outward appearance scarcely differing 

 from the common slug, but distinguished by carrying a small 

 shell above the tail ; and a species of Vitrina, or shelled ter- 

 restrial snail, found under stones in moist, shady, or grassy 

 situations in the higher parts of the Island of Madeira. 

 Unlike the slugs, the Testacellus burrows in the soil, and is 

 the dread of the earthworm on which it feeds ; and these 

 habits are accompanied with corresponding changes in its ' 

 organisation. Its body is more cyhndrical than that of the 



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

 membranes arc 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 ; so that the great side, or basis, is set into the mem- 

 brane of the gizzard, as a diamond in its socket. Otiicrs 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 , 1768, p. 587. 



+ De Anim. Mar., p. 19 and 22. % Darwin's Journal, iii. 6. 



§ Cuv. Mollusq. Mem. ix. 18. 



