67 
reject Dr. Gray’s hypothesis. Our late excellent associate, 
Dr. 8. P. Woopwarp, of the British Museum, always strenuously 
opposed this view of the subject. Nevertheless, in order to 
chase away all doubt, I have consulted Professor HUXLEY, 
whose account (see article “‘ Mollusca”) containing the history 
of the development of that sub-kingdom ought to be studied by 
every one who concerns himself about the matter. The Pro- 
fessor kindly writes to me in reply—‘I have not the slightest 
doubt that Dr. Gray was wrong and Woopwarp right about the 
operculum of Gastropods.” And moreover, Professor HuxLEy 
considers “that the development of the part is conclusive upon 
the point.”* We may therefore infer most safely from this 
departure that the correspondence of the operculum as to 
funetion would be like that of the plug in certain of the Bysso- 
arca, which was the opinion of Professor Forsss ; and that it 
corresponded in position to the byssus of other Conchifera, 
according to Loven, though of much more complex structure. 
(S. P. Woopwarp.) 
A few words may be allowed on the position of the operculum. 
It is attached to the posterior part of the foot of the animal, 
and is there developed, and not secreted by the mantle like the 
rest of the shell. When the animal has withdrawn into the 
body-whorl of its shell, this part ingeniously forms a perfect 
shutter to the orifice, generally fitting it with a marvellous 
closeness,—though in some species it does not wholly close the 
aperture, but only serves as an imperfect defence to the animal, 
like the puny buckler of certain African savages ; indeed, when 
the substance of the opercula, as in many species, is horny 
instead of shelly, the protection they afford can avail but little. 
For instance, the fine Ampullaria insularwm, a large fluviatile 
Gastropod that flourishes in the muddy marshes of La Plata, is 
Ae aa 
* I would quote the Professor’s expression of opinion in his lectures, 
which I did not happen to meet with until lately. Treating on the Branchio- 
gastropoda (GREENE), he states that ‘as the operculum is developed from 
the foot, and not from the mantle, it can obviously have no homology with 
the valves of either a Brachiopod or a Lamellibranch.” —Hux.eEY, Lectures 
on Comparative Anatomy, p. 36. London, 1864. 
F2 
