60 MR. T. H. HUXLEY ON THE MORPHOLOGY OF THE CEPHALOUS MOLLUSCA. 
the portion of the molluscous type here considered*, and indeed to be peculiar to it. 
Its occurrence in Chiton, therefore, would effectually determine the molluscous 
nature of that genus, even if there were no other grounds for the conclusion; while 
the structure of the buccal armature of Sagitta, which has been compared to the 
protruded tongue of a Heteropod, is in fact so totally different as at once to lemove 
it from the Moiluscaf-. 
I may further remark, that the structure of the tongue in the Cephalopoda adds 
one more link to the very strong chain of affinity between them and the ordinary 
Mollusca. 
Of the Pyloric Sac. — This appears in various forms in a great number of the Mol- 
lusca, and seems to be always in special relation with the liver. In Atlanta, it has 
been seen that its glandular parietes form the liver. In the Cephalopoda the hepatic 
ducts enter its representative, the spiral sac of Octopoda, the elongated sac of Loligo. 
The extreme length of the pyloric sac in Cleodora, and the occuiience of a second 
smaller one, appear to be leading the way to the ramified prolongations of the 
intestinal canal found in the Eolidce. 
In Pteroceras a very remarkable structure exists, which, so far as I am aware, has 
not yet been noticed The existence of a ‘‘crystalline style” in connexion with the 
alimentary canal, has long been known in the Lamellibranchiata, but it has hitherto 
been supposed to be confined to them. However, in Pteroceras, the pyloric sac con- 
tains a very complete style, Plate V. figs. 16, 17- 
The stomach is a wide somewhat quadrangular cavity. The oesophagus opens into 
* It has been noticed by Teoschel (Anatomie von Ampullaria Urceus, Wieg. Arch. 1845), that the struc- 
ture of the tongue is the same throughout those Mollusks which have a head ; “ Under the jaw lies the anterior 
part of the so-called tongue, a membrane which is present in all Pteropoda, Cephalopoda, Gasteropoda, in short, 
in all those Mollusks which possess a head. It is wanting in all the so-called Acephala, m the Bivalves and in 
the Tunicata. It rests, as in all cases where it is present, upon two portions of cartilage of whitish colour, 
combined by a membrane and moved by many muscles.” It is clear, however, from this passage, that Teoschel 
has not recognized the true mechanism of the organ. 
t There is a curious similarity between the “ tongue” of the Mollusca and the arrangement of the dental 
apparatus in the Plagiostome fishes, which may be viewed perhaps as another illustration of Von Baek s la%v, 
that while the exterior of a vertebrate animal is Articulate in its construction, the interior is Molluscous. 
j; Since writing the above, I find that so far back as 1829, the existence of this organ was distinctly pointed 
out, though strangely enough the fact has been quite overlooked by every one save Von Siebold ; he, however, 
merely refers to the statement in a note, and says he “does not know what to make of it. (\ eigleichende Ana- 
tomie, p. 312.) This statement is contained in a valuable paper upon the anatomy of the Mollusca, entitled 
“ General Observations on Univalves,” by Mr. Chaeles Colliee, StafF-Surgeon at Ceylon; printed in the 
Edinburgh New Philosophical Journal for 1829, p. 231. “ There is an organ, the crystalline stiletto, confined 
erroneously by a celebrated naturalist (Cuvier) to bivalves, which is found in every sjiecies of Strombus, in Tro- 
chus turritus, and a species (^Vertagus) of Murex. It is enclosed in a sheath, that passes parallel to and by the 
side of the oesophagus, to the stomach, into which the stiletto enters, leaving its covering ; that end whieh lies 
within the stomach is obtuse, laminated, and fixed by a hook of similar substance to its situation. Ihe upper 
portion is circular, homogeneous, slightly tapering, transparent, of gelatinous consistence, and resembling some- 
what a pistil with its stigma.” 
