consider it a northern form, but our knowledge of foreign species is much too limited to
allow of our pointing out their geographical distribution with any degree of certainty.
The body of Eolis is limaciform, in some species rather depressed and ovate, but more
generally slender, and nearly linear when extended. The back is rounded, and has no
vestige of cloak: the skin is thin and smooth, without spicula. The head is terminal, and
scarcely distinct from the body, into which it passes imperceptibly: it is provided with four
linear non-retractile tentacles, of which two are dorsal and two labial or oral. The dorsal
tentacles are frequently ringed or wrinkled, rarely laminated, but in the greater number of
species they are smooth, and only slightly wrinkled when contracted. The eyes are placed
behind them. The oral tentacles are always simple, arising either from the margin of
the lip or a little above it. A third pair of tentacles is mentioned by Cuvier, but these
are merely the elongated margins of the foot. The mouth is sub-inferior, and provided with
strong corneous jaws. The branchiae are elongated, cylindrical, ovate or flattened processes,
usually called papillae, arranged in transverse rows on each side of the back, and leaving a
naked space more or less visible down the centre: these rows are in some species grouped
into clusters. The foot is usually nearly linear, and grooved in front, the anterior angles
being in some species produced into long tentacular processes, which may occasionally be
used as feelers, but analogy forbids our considering them as true tentacles. They probably
assist progression. The aperture of the generative organs is placed forwards on the right
side, and the anus is a little behind and above on the same side, generally near or between
the branchiae: it is very inconspicuous, and escaped the observation of Cuvier, who states
that this and the generative organs are united in one common orifice.
The members of this genus are all carnivorous, feeding on zoophytes and other small
marine animals. Some of them are very voracious.
The genus may be divided into four sections, characterized as follows:
Sec. 1. Branchial papilla numerous, depressed, and imbricated. E olis proper. Type, E. papillosa.
In this section the body is rather broad and ovate; both pairs of tentacles shortish 'and
smooth ; and the sides of the foot a little produced and pointed.
Spaum consisting of numerous much-waved coils.
Sec. 2. Branchial papilla clustered. F labellina, Cuvier. Type, E. coronata.
The body is slender and rounded above; the dorsal tentacles generally ringed or wrinkled ;
the oral tentacles long ; and the sides of the foot produced into linear processes.
Spawn consisting of many coils, sometimes waved.
This section may be divided into three sub-sections.
* Dorsal tentacles ringed or laminated. Type, E. coronata.
* * Dorsal tentacles wrinkled or smooth. Type, E. gracilis.
* * * Dorsal tentacles bulbed. Type, E. alba.
Sec. 3. Branchial papilla in transverse, generally rather distant, rows. Cav o l in a, Bruguière. Type
E. cingulata.
The body is a little broader than in the last section; the dorsal tentacles smooth or
wrinkled ; the oral tentacles shortish; and, the sides of the foot slightly produced and
rounded.
Spawn consisting of one or, at most, two coils.
This section also contains three sub-sections.
* Papillae sub-linear, rows rather close. Type, E. concinna.
* * Papillae sub-linear or slightly inflated, rows distant. Type, E. cingulata.
* * Papillae large and inflated. Type, E. tricolor.
Sec. 4< Branchial papilla in a single longitudinal row on each side. Tergipes, Cuvier. Type,
Ei despecta.
The body is linear; the dorsal tentacles smooth, the oral tentacles very short; and the
sides of the foot rounded and not produced.
Spaum kidney-shaped.
In sections 1 and 2 the auditory capsules contain numerous otolithes; in section 3
they contain only one otolithe each.*
These sections run imperceptibly into each other, but in general their characters are
pretty well marked. The branches of the digestive system undergo a modification in each'
section corresponding to the arrangement of the papillae, as mentioned below.
As Eolis is the type of a family whose anatomy, from its peculiar character, has
attracted some degree of attention, we purpose entering rather more into detail than we
should otherwise have done: for more complete details, however, we must refer those of our
readers who are interested in the subject, to the ‘Anatomy of Eolis,’ published by one of the
authors of this work in conjunction with Dr. Dennis Embleton, in the ‘ Annals of Natural
History,’ of which the following is little more than an epitomy.
The digestive system shows in some parts great divergency from the molluscan type.
The mouth opens on the inferior surface of the head, and has large fleshy lips, divided
vertically and prolonged into an internal tube, within which is a circular band of strong
muscles forming an inner lip, capable of being pushed forwards, and bringing with it the
mouth and jaws, when the animal is in the act of seizing its prey. The mouth contains two
large horny jaws, placed vertically and nearly co-extensive with the fleshy sides of the
buccal mass. They are of an irregularly elliptical or ovate form (PI. 8, figs. 17, 18, 19), a
little produced on the upper anterior margin, where they are united by a strong ligament
forming a hinge-like joint on which they move: below this two strong arched processes
extend downwards in front, forming the cutting edges of the jaw. The tongue is strap-shaped,
and covered with numerous transverse plates, armed with spines or teeth directed backwards;
it is attached through its whole length to a wedge-shaped muscular mass, convex above, and
extending to the entrance of the oesophagus (PI. 7, figs. 5, 6). The muscular arrangements
by which the tongue is moved in different directions, and can be thrown forwards to assist
the animal in seizing and securing its prey, are beautifully adapted for the purpose, but it
would lead us too much into detail to describe them here.f The lingual teeth differ in
different species; in E . papillosa they are small and very numerous, forming transverse
arched rows (fig. 7); in E. coronata there is one large central tooth on each plate, with
denticulated sides; and in E, alba a central tooth only, without denticulations (figs. 11, 12).
These teeth are very minute. In E. papillosa they are not more than one sixth part the
thickness of a human hair; they are often found broken abruptly off, but never bent; and,
from the circumstance of their resisting all acids but the hydrofluoric, there can be little
doubt that they are siliceous. The salivary glands (fig. 6 a) are very small, and placed*
between the corneous plates and the muscular mass of the cheek. The gland is composed of
* The capsules in the 4th section have not been examined, but as far as our observations go in
the other three this distinction is without exceptioii.
f See Hancock and Embleton's f Anatomy Of Eolis/ Ann. Nat. Hist, xv, 6.