384 Dr. Reid on the Development of the 
In the bottom of this anterior notch, immediately in front of the 
point where the thickened margins of the discs become conti- 
nuous, and at the base of the upper surface of the foot, the mouth 
(fig. 16 y), which is formed by a simple rounded aperture, is 
placed. The long cilia attached to the outer edge of the upper 
surface of the thickened margin of the dises are when at rest first 
bent inwards at an acute angle as far as the inner edge of the 
thickened margin, and then project upwards and outwards, but 
become more straight when in a state of action. The upper 
surface of the foot and the sides of the mouth are provided 
with cilia considerably smaller than the locomotive ones attached 
to the margin of the disc, and still smaller cilia are placed upon 
the hollow upper surface of the discs and other parts of the em- 
bryo outside the shell. Two very obvious and transparent cells 
(figs. 16 and17), possessing much more refractive power than the 
other parts of the embryo, are placed in the base of the foot, at 
the sides of the gullet and immediately below the mouth. Hach 
of these is apparently inclosed in a larger cell; at least each of 
them is surrounded by a well-defined ring, which however is more 
opake than the cell which it encircles (figs. 20 and 21*). From 
the mouth the gullet leads downward and forwards to the stomach 
(fig. 20 h), and from the back part of the stomach the intestine 
(fig. 202) commences. The intestine bends to the right, pro- 
ceeding upwards on this side, and terminates a little below and 
behind the right transparent cell in the root of the foot, and it is 
there surrounded by a portion of an irregular mass composed of 
a few cells (fig. 20 0) occupying that position. The whole of the 
inner surface of the gullet, stomach and intestine is covered with 
cilia, and in some cases, masses, chiefly composed of what ap- 
peared to be minute cells thrown off from the inner surface of the 
digestive tube, were revolving rapidly in the stomach. Two 
masses adhered to the lateral surfaces of the stomach and lower 
part of the gullet (fig. 20 m and n) ; one of these, by much the 
larger (m), was placed on the left side, and projected considerably 
in front of the stomach; the other adhered to its right side (), 
and was placed immediately in front of the upper part of the in- 
testine. Hach of these two bodies was composed of a single cell 
only, having minute cells or nuclei similar to those originally 
composing the ovum, scattered over its inner surface with consi- 
derable intervals between each. In several cases some minute 
* Van Beneden supposes that these transparent cells which he observed 
in the embryo of the Asplysia may be the rudiments of the nervous System. 
This opinion may be true, but at present it must be considered only in the 
light of a supposition. ‘These cells, if 1 mistake not, may be occasionally 
seen vibrating slightly within the larger cells inclosing them. It has been 
suggested to me that these may be the rudiments of the auditory organs. 
