able. Sometimes the ground colour is yellowish and the mottlings light, leaving a general
impression of yellowish brown. Sometimes the mottlings are thick and dark and the
ground colour opaque white. The upper surface then appears to be purplish black, with
a few white markings.
The animals are stoutly* built, the largest specimens measuring 5‘5 ram. by about 3*5
mm. In front the dorsal surface is bare, the cerata being set only at the sides, but behind
they close over the body. The foot is white, broader than the body, with an expanded
margin, but rather straight in front. No anterior groove is visible. Hancock made
several drawings of the animal, besides those here reproduced, which indicate that the
shape of the frontal margin varies considerably. It is sometimes represented as straight
and sometimes as notched or bilobed. Probably the animal when alive can alter its
outline.
At the sides there is a groove between the body and this margin, so that the
body, though narrower than the foot, partly overhangs it. On this lateral projection of
the body are set the cerata in three not very regular longitudinal rows. As a rule only
two rows are fully developed, and the third, which consists of smaller cerata, has the
appearance of being crowded in. The total number of cerata on either side does not
appear to exceed fifteen, which is less than the number shown in Alder and Hancock’s
plates. The cerata are somewhat ovate in shape. Those behind are larger and more
inflated than those in front. They contain ramified hepatic diverticula which-bear
primary and sometimes short secondary branches.
The head bears on each side a rounded prominence, but there are neither rhinophores
nor tentacles in the ordinary sense. The anus is on a prominent papilla in the medio-
dorsal line and nearly terminal.
There is no trace of jaws. The radula is ascoglossan and short, containing five or
six teeth in the ascending, and about as many in the descending portion. In an irregular
heap lie about seven teeth of varying size, and with them a mass of minute spines,
apparently representing the first teeth. The mature teeth are large and spoon-shaped.
The outline is rather irregular, and there are generally two more or less distinct projections
on the back.
There is no crop attached to the buccal mass, but from it issues a thin tube which
must apparently be regarded as equivalent to a stomach as well as to an oesophagus, at
least in its posterior part, for from it arises the intestine. This is a larger tube which
bends slightly to the right and then runs directly backwards at first on the right under
the side of the pericardium and finally above the renal organ to the anal papilla. The
thin tube issuing from the buccal mass bears two folds inside. At its posterior extremity
these folds become more numerous, and the tube bends downwards and dilates into a large
stomach-like pouch. It is clear, however, that the intestine does not issue from this
pouch, but from the narrower tube. It is probable that the animal lives on vegetable
juices, and that the two folds in the tube act as strainers and valves, establishing communication
alternately between the mouth and the pouch and between the pouch and the
intestine, only one line of communication being open at a time. The pouch is prolonged
anteriorly under the oesophagus, and divides into two diverticula which enter the anterior
lobes of the foot. Posteriorly it extends almost to the end of the body and gives off two
sets of ramifying diverticula. The upper diverticula (about four in number) enter the
cerata and are also ramified in the body. The lower diverticula (also about four) extend
downwards through the hermaphrodite gland and do not enter the cerata, but their ramifications
within the body create the peculiar dendritic markings visible through the sole
of the foot.
The central nervous system (PI. VII, fig. 6) forms a collar round the oesophagus
consisting of seven principal ganglia close to one another and connected by very short
commissures, the longest being that connecting the cerebral ganglia. They should
probably be regarded as two cerebral, two pedal, and three visceral ganglia. Connected
with the cerebral ganglia are two smaller ganglia, probably rhinophorial in function and
innervating the most sensitive part of the head, although no external rhinophores are
developed.
The hermaphrodite gland is large and ramified throughout the whole lower part of
the body, filling up the interstices between the other organs. The ampulla and duct of
the gland are short. .After the bifurcation of the male and female branches the former
runs to an orifice at the right anterior corner of the head. The vas deferens is not very
loijg or much convoluted. A rather large prostate opens into it by several ducts. The
penis is armed with a rather long curved spine, which in some specimens at any rate points
inwards when the organ is retracted. Shortly after the bifurcation the female branch
receives a long duct into which open the follicles of the albumen gland. This gland, like
the hermaphrodite gland, is extensively ramified, especially in the last fourth of the body.
Close to thé entry of this duct and lying anteriorly is a pouch-like diverticulum which is
probably a spermatotheca. No second spermatotheca was found. The female branch
here makes a sharp turn and runs backwards nearly to the end of the body; it then
doubles on itself and runs forwards, opening anteriorly close to the male orifice. All this
section of the female branch after the spermatotheca is very much larger than the other
parts and provided with remarkably thick glandular walls. It should probably be
regarded as the uterus passing through the mucus gland. I t is one of the largest and
most conspicuous organs in the animal, and when sections are cut it generally expands
and overlaps the heart and kidney.1 This, however, appears to be the result of the
disturbance caused by the cut, and not a natural arrangement. It is noticeable that near
the bifurcation of the male and female branches there arises a cæcum which extends
anteriorly and reaches the integument, but without forming any orifice. Pelseneer states
(1, p. 62) that in JElysia the second female orifice is developed later than the others and
is not found in young individuals. I t is conceivable that this cæcum in Alderia may
ultimately open externally. «
The pericardium appears to be as usual and is medio-dorsal. The renal organ
lies below it and is entire in the front, but the posterior portion gives off ramifying
tubes, some of which extend into the cerata.
Blood lacunæ are distributed throughout the body, including the foot. The largest
lie one on either side of the renal organ below the cerata, into which they send up long
diverticula ; the main portion of these diverticula lies on the posterior side of the cerata,
1 This dislocation seems due to the elasticity and expansive power of the tissues which form the
walls of the uterus.