DIGESTIVE ORGANS. 91 



is so large that it will admit a goose-quill, and which is divided 

 into many branches throughout the foot, which open, by means 

 of numerous finer branches, into the abdominal cavity. Agassiz 

 injected carmine or indigo solution through this pedal pore, and 

 •it filled not only the pedal canal system, but also the body- 

 cavit}' and, finally, the whole vascular S3^stem. Quite similar 

 relations were found by him to exist in the bivalve genus Mactra 

 (vii, 86). The water actuall}^ mixing with the blood in this 

 manner, Agassiz also showed thereby that the blood was exhaled 

 from the bodj^-cavity, salt crj'stals also being observed, which 

 were derived from sea-water which had been taken up. It has 

 been known for a long time that univalves when removed from 

 the water allow considerable water to escape from them, which 

 runs out of the foot. Agassiz found numerous blood-corpuscles 

 in this water, and there can, therefore, no longer be any doubt 

 that water passes through the pedal pore into the abdominal or 

 body-cavity, where it is mixed with the blood. 



On the other hand, the researches of Mr. Wedl have led him 

 to announce the existence in the mollusca of a completely closed 

 vascular sj'stem, with capillar^^ networks in the greater part of 

 the organs. The tjqje of distribution of these is extremely 

 variable, and intimately connected with the structure. It is thus 

 that in the Murioes the skin of the trunk and of the back is 

 formed of several superposed layers of muscular fibres, crossed 

 in diflerent directions, and that several networks of blood-vessels 

 are likewise superposed in these parts. The vascular networks 

 are superposed in the same manner in the foot of these cteno- 

 branchs. In no part of the skin is there an}" communication 

 between the veins and the exterior ; nor do the veins appear to 

 communicate with the aquiferous vessels. M. Wedl, however, 

 has not been able to determine whether these last open directly 

 into the perivisceral cavity, or whether the}' are distributed only 

 in the foot, — Sitzung>:b. Akad. Wins. ('F^■e•.•, ii, 1868. Ann. Mag. 

 Nat. Hist.., 4 ser., iv, 365. 



DIGESTIVE ORGANS. 



Cephalopoda (ix, 93, 94). The organs of manducation in the 

 Cephalopoda include a corneous or calcareous beak resembling 

 that of a parrot reversed ; within which is a fleshy tongue armed 

 with teeth. These parts are enveloped in a large muscular hulh 

 which supplies the force to the jaws. External to the beak are 

 two lips, themselves surrounded and protected by an extensible 

 buccal membrane (iii, 48), situated between the buccal bulb and 

 the bases of the arms. The buccal membrane, wanting to the 

 octopods, is well marked in the decapods. In development it 

 forms a vast funnel, and in repose it covers all the exterior part 

 of the mouth. It is encircled by eight or ten fleshy appendages. 



