Prof. G. J. Allman on the Anatomy of Acton. 151 
sally diffused over the soft and constantly lubricated skin of the 
mollusk, yet it would appear that the tentacula are specially ap- 
propriated to its exercise. These organs consist in auriform 
expansions rolled into a cylindrical tube, Pl. V. figs. 1 and 2, but 
capable of being to a certain extent opened out at the will of the 
animal. They are incapable of undergoing any true retraction, 
but may be slightly shortened and thickened, in which condition 
they present a number of transverse rugee. They are supplied 
with large nerves from the supra-cesophageal gangha. No fact 
has thrown any light upon the question whether another sense 
besides that of touch has also its seat in these organs. 
The entire surface of the skin is copiously lubricated with a 
thick mucous secretion, which is poured out in large quantity 
when the animal is irritated. The source of this fluid would seem 
to be in certain pyriform bodies, Pl. VII. fig. 8, which are found 
in considerable numbers beneath the tegument. Hach termi- 
nates in a sinuous duct, which after running for some distance 
beneath the skin, opens, most probably, upon the surface. These 
organs are described and figured by Quatrefages, but the French 
naturalist is in error when he speaks of them as the source of 
the beautiful metallic tints with which the surface of our mollusk 
is adorned. These tints are due to a pigment inclosed in distinct 
cells, arranged in irregular groups beneath the epidermis, consi- 
derably smaller than the bodies just described, and evidently 
without any duct or external communication whatever. I am 
unable to bring forward any observations of interest relative to 
the senses of taste and smell in Act@on. 
Generative system: Embryology.—The reproductive system of 
Act@on is one of great complexity, and one in which there must 
be great difficulty in assigning to each part its proper function. 
Acton is hermaphrodite. A pyriform body, Pl. VI. ¢, placed 
anteriorly and at the right side, would seem to be the male in- 
tromittent organ. ‘This body is furnished with a tubular perfo-= 
ration which occupies the axis, and leads from the apex into an 
oval cavity, v, situated in the base. From this cavity a simuous 
tube, or vas deferens, w, may be traced backwards, which, after a 
course of considerable length, communicates with an oval body, z, 
to be presently described, and then pursuing its course backwards 
may be seen to bifurcate, one branch passing to the right and the 
other to the left. Beyond this point I have in vain attempted 
to trace the course of the tube. Its whole internal surface is 
thickly clothed with cilia, whose presence is rendered manifest 
by the constant rotatory motion imparted to the granular fluid 
with which the tube is filled. 
Occupying a median position in the posterior part of the body 
is an oval sac, y, near whose anterior extremity two tubes may be 
