rather broad and expanded; deeply grooved in front, and terminating in a point behind.
The aperture of the genital organs is placed near the middle of the right side.
The single species on which this genus is founded occurs on the coast of Italy and on
the southern shores of England. It belongs to the Laminarian, and perhaps extends into the
coralline, zone; it is undoubtedly carnivorous, as we have taken from its stomach the
remains of some mollusk, probably that of a nudibranch.
A detailed account of the anatomy of this genus has been published by M. Blanchard in
the Annales des Sciences Naturelles ;’* the following description of its internal structure,
however, is derived entirely from our own examination of specimens procured from both the
Mediterranean and the British shores; and it will be seen that, in several important
particulars, we are unfortunately at variance with that naturalist.
The genus varies much in its anatomy from Eolia. The buccal mass (PI. 43, figs. 1 a
and 2 a) is exceedingly large, a little depressed, and somewhat lozenge-shaped. The jaws
(figs. 3, 4) are likewise of great magnitude, and are not mere thin laminae; but are of
considerable thickness, of a triangular form, and each is furnished in front with a powerful
denticulated cutting plate (a), having, immediately within and parallel to it, another cutting
edge (i), w^ich is plain. The tongue (fig. 5) is broad, and formed as in Doris, with the
posterior portion tubular. The spines (figs. 6, 7), which are simple, are, in A. cristaia,
arranged in thirty transverse rows, inclined forward, each row containing eighty spines, and
there is a central, equally large and plain spine in each row.
The oesophagus (fig. 2 It) is wide, internally plicated, and very short; it opens into a
distinct gastric pouch or stomach (c), placed in the anterior portion of the body. The stomach
is transversely elongated, and has the upper wall so thin and delicate, that the internal plicse
are distinctly seen through it. On the lower portion, and towards the left side, where the
intestine leaves the stomach, there is a thin coating of a glandular structure (d). The
intestine (fig. Id , fig. 2 e) is very wide, and doubling back upon the stomach, passes
diagonally to the right side of the body, down which it is continued, for some distance, and
then, dipping beneath the posterior lobe of the ovary, reaches the large anal nipple, (fig. 1 e,
^ f ) on the median line of the back near the posterior extremity.
Two principal hepatic trunks open into the sides of the stomach above. On leaving that
viscus, these almost immediately divide into two branches; the anterior (fig. 2g,g) of which
pass round in front of the head, and are united on the median line. These two branches
communicate by various ramuscules, with the glands of the anterior papill®. The other or
posterior branches (ft, h) of these hepatic trunks curve backward, and are connected in like
manner to the numerous papillm on the sides, extending more than half way down the body.
Here these branches terminate. The posterior papillm of both sides communicate with a
median trunk tube (i), which, dipping under the anterior ovarian lobe on the left side, passes
forward, and opens into the lower glandular aspect of the stomach, a little in advance of where
the intestine leaves it. All the principal tranks and branches are of a dark colour, when
the animal is alive. The median trunk tube corresponds to the great central hepatic duct
m Eolis, while the branches from the upper surface of the stomach are equivalent to the
anterior ones of that genus, which always open into the dorsal aspect of the digestive sac.
* 3d Series, vol. x, p. 72.
M. Blanchard does not appear to be aware that any such median trunk tube exists in
this animal; we have, however, on more than one occasion determined its presence by actual
dissection.
The hepatic gland of the papillae (fig. 8) is peculiar in its structure; it is comparatively
small, and lies within an inner sheath; the lower portion is narrow and tubular, the
termination bifid, with each division slightly branched and folliculated, forming a beautiful
example of glandular organisation reduced to its simplest element. Delle Chiaje has
described a terminal vesicle with urticating filaments in the apex of the papillae, as in Eolis.
This has escaped our observation, though a distinct external orifice was visible in the living
state.
The glands of the papillae do not appear to be the only representative of the liver in this
genus. On each side of the lower portion of the body, immediately within the skin, there is
a peculiar glandular structure, composed chiefly of anastomosing tubes (fig. 1 h, h), which form
a network across the dorsal aspect in front of the anus. This network inosculates with the
minute hepatic branches leading to the papillae, and is also apparently connected with a dense
gland-like body (a), surrounding the termination of the intestine. There can be little doubt
that this network of tubes is a part of the hepatic organ ; and from its internal position, it
points out Antiopa as one of the intermediate forms uniting the Eolididcs with the other two
families of the order. The tongue, also, of this genus is interesting, as evincing the same fact.
The vascular system apparently resembles that of Eolis, with the exception of some
variation in the disposition of the branchio-cardiac vessels. We have observed two trunk-
veins opening into the posterior margin of the auricle, and M. Blanchard represents several.
In the Eolides there is only one trunk-vein so situated; neither is there anything like this
arrangement in either Boris or Tritonia. The heart is placed about the middle of the back,
directly below the skin ; having the intestine in front, and the ovary beneath. The ventricle
(fig. ly) is large and strong, the auricle (k) thin and delicate: they are contained within a
pericardium of great tenuity, having, lying beneath its floor, a vesicle (l), which in Boris we
have called a portal heart. In this instance, the vesicle opens through the lower wall of the
pericardium in the same manner as that does in Boris; and, as in that genus, its internal
surface is plicated. We have not been able to carry the comparison further; but suppose
that this additional heart in Antiopa may supply the internal hepatic network with venous
blood, and perhaps also the glands of the papillae.
The branchial papillae are very delicate, large, and numerous in this genus. They will
undoubtedly be assisted in aerating the blood by the general surface of the body.
The cerebroid and branchial ganglia (figs. 10 a, a, b, 6) are fused into one, and thus, on
each side of the median line, there is an elongated mass, as in Eolis; but being more distinctly
bilobed, the constituent parts are easily determined.
The pedial ganglia (c, c) are almost circular, and are placed external to, and only a little
below, the others. The olfactory nerves (e) are very large, and come, as usual, from the
upper surface of the cerebroid ganglia; they divide into two portions, those next the median
line converge and go to supply the crest at the base of the dorsal tentacles; the other
portions are sent to the tentacles themselves, within the base of which they terminate in
the olfactory ganglia (d, d). These are of a circular form.
There is nothing peculiar in the other nerves of the supra-oesophageal ganglia, except