The species in the first section show varieties of structure, that might admit of farther
subdivision, but the British forms contained in it are so few, that we think it unnecessary at
present to carry the analysis further.
Cuvier has given a description and figures of the anatomy of Doris in the c Memoires des
Mollusquesbut these, though sufficient for the purpose then contemplated by the great
physiologist, do not go much into detail. It seems desirable, therefore, to extend our
observations in the present work; and for that purpose we have, with the assistance of our
friend Dr. Embleton, made careful dissections of the various groups of the genus, and shall
now give the results of our investigations at some length, as in this instance they relate to
the typical member of a family.
The mouth opens in front between the cloak and foot, and conducts by a short
constricted channel (PI. 1, fig. 6 e), which is provided with an outer (c) and an inner lip (d),
to the buccal mass. This is a highly developed organ, of an irregular oval form, the walls (p)
being composed of numerous strong muscles, some to assist in the motions of the tongue,
others to aid in carrying the whole apparatus to and from the oral aperture.
The buccal organ varies to some extent in our three sections; in the first (PI. 2, fig. 1 a)
it is simple and well developed; in the second (PI. 1, fig. 13 b) it is small, and has in addition
a large, circular, and beautifully organised muscular gizzard (c) attached to its upper surface,
into which this gizzard opens a little in front of the oesophagus. The gizzard is very
peculiar, and we believe nothing like it has been hitherto noticed. It is somewhat lentiform,
with the walls very thick and firm, smooth in the interior, having the sides externally covered
with regular radiating muscular fibres, and a strong muscular belt encircling the margin.
This modification is observed in D. bilamellata, D. aspera, and D. depressa. In the third
section the buccal apparatus (fig. 12 b) is very large, being apparently an incorporation or
blending of the ordinary buccal mass, and the gizzard (c) of section 2. It is anteriorly
enlarged and rounded, with the channel (a) of the mouth opening into it on the under surface,
and not in front, as in the other two sections (fig. 13 a).
The tongue (fig. 6 i) consists of a tubular dentigerous membrane, the upper portion of
which is partly enclosed within, and partly expanded upon a conical muscular mass (h),
(the lingual muscles), the base of which occupies the floor of the mouth, the apex pointing
forwards, and the expanded dentigerous surface being opposed to the oesophagus. The lower
part of the tongue is prolonged into a delicate pouch (fig. 3 m), which projects beyond the
posterior and under part of the buccal organ. In this pouch is generated the membrane,
which in its turn gives origin to numerous recurved teeth or spines in rows, which, as they
are formed, are, together with the membrane, gradually pushed onwards; and as those before
them are worn away or broken, they successively ascend, and eventually reach the upper
expanded part of the tube, which is spread out upon the upper surface of the conical mass
of lingual muscles. It is this upper part of the tube (figs. 4 and 7 a), expanded like the
mouth of a trumpet, that alone performs the office of prehension; the other, more
strictly tubular portion (b), of considerable length in some species, is that in which the
teeth are developed, perfected, and retained until brought into connexion with the muscular
apparatus.
In the first section the tongue is broad (fig. 7), and the rows of teeth transverse. In
D. tuberculata the rows are forty four in number, each row comprising one hundred and forty
simple teeth (figs. 8, 9). There is no central tooth in this species, any more than in
D. Johnstoni or D. coccinea, in both of which the teeth are likewise simple ; but in the former
of these the outer teeth suddenly become excessively attenuated, and in the latter attenuated
and elongated. D. Johnstoni has twenty-four rows, each of about fifty teeth. The tongue of
D. repanda is provided with a central tooth (fig. 10«) bearing four recurved denticles, and
has the lateral teeth (figs. 10, 11) with regularly serrated sides. This species has sixty-eight
rows, of thirty-seven teeth each, In our second section, represented by D. bilamellata and
D. aspera; and in our third section, typified by D. pilosa, the tongue (Fig. 3 1, and Fig. 4) is
narrow and strap-shaped, being composed of only two rows of teeth, and these placed
longitudinally. In these species, therefore, this organ, having a wedge-shaped muscular
support (fig. 3 k), has a general resemblance to that of Eolis. It is nevertheless essentially
formed as in other Dorides, and has the posterior portion tubular (fig. 4 b). The two rows are
of lateral teeth, the central ones being entirely deficient. There are twenty-eight teeth (fig. 5),
in each row in D. pilosa, with the sides minutely denticulated. The teeth are equally numerous
in D. bilamellata, but the sides are plain.
Besides the tongue, some of the Dorides are provided with a spinous prehensile collar
(fig. 3 h), situated at the entrance of the buccal apparatus, and placed in a vertical position on
what may be termed the buccal lip ip). This collar is of nearly uniform breadth in D. repanda,
and is densely covered with minute, curved, bifid spines. In D. pilosa it is provided with
similar spines (PI. 2, figs. 3, 4, 5), and is divided into two lateral portions (fig. 2 b, b), broad
below, and tapering to five points above. These two portions of the collar have, intervening
between them below, two minute triangular processes -(c) of a horny plate (fig. 6), which is
buried in the buccal lip, having only the free points exposed; these are inclined upwards and
forwards. This plate with its processes may, perhaps, be looked upon as the homologue of
the jaws in Eolis; though this relation may admit of doubt, nevertheless it appears to be
accessory to the prehensile action of the collar. The prehensile collar and jaws of D. subquadrat
a closely resemble those of D. pilosa. D. bilamellata is provided with a similar horny
plate and processes, but much less developed, and the collar is very indistinct, having the
surface only roughened with dense, minute wrinkles. D. coccinea is also furnished with a
spinous prehensile collar. These five are the only species in which we have detected this
curious organ, which is probably a compensation for the deficiency of well-developed jaws.
A pair of salivary glands (fig. 1 h), generally in form of long slender tubes, open into
the mouth, one on each side of the oesophagus; D. bilamellata has these tubes replaced by a
follicular mass (PI. 1, fig. 13 e) attached to the posterior part of the buccal apparatus; and in
D. pilosa they (fig. 12 d) are enlarged and folliculated at their bases.
The oesophagus (PI. 2, fig. 1 b) in D. tuberculata is a nearly straight tube passing from
the posterior dorsal aspect of the buccal organ; it is slightly enlarged after passing through
the nervous collar, and is then continued on, of equal diameter, to the posterior or cardiac end
of the stomach, which (PI. 1, fig. 2 b, and PI. 2, fig. 1 c) is a very large pyriform pouch,
having the inner surface minutely corrugated. It lies on the left side of the body, and has the
narrow posterior end resting between the lobes of the liver. Here the biliary fluid is poured
in by a large canal (PI. 2, fig. 1 g), and at this part, too, a small pancreatic organ (i) gives its
secretion to the stomach by the side of the oesophagus. The intestine (d, d) leaves the