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- 

 nuouSj 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 discs are when at rest first 

 bent inwards at an acute angle as far as the inner edge of the 

 thickened m«irgin, 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 and 17^), 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. Each 

 of these is apparently inclosed in a larger cell j 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)f and from the back part of the stomach the intestine 

 (fig. 20 i) 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 o) 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 ofi" 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 {n), 

 and was placed immediately in front of the upper part of the in- 

 testine. Each 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 Asply.sia 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. 



