has been more fully described by the Rev. R. T. Lowe in his very curious genus Peplidia,*
found on the shores of Madeira. Mr. Lowe’s graphic description is of so much interest that
we are induced to give an extract of it. “ In a glass of sea-water in which this animal lived
for more than.six weeks, it had the usual habits of a Doris, but with more activity: swimming
about violently when disturbed or when provided with a fresh supply of water, in which
operation the hind part of the body, with the crested fin-like tail, is lashed from side to side
with a strong and regular sculling motion; the fore-part, with the head or veil expanded to its
full dimensions, being at the same time beat with equal force and regularity in a contrary
direction, or obliquely upwards and downwards, stroke for stroke; these parts (the veil and
crest) performing thus alike the office of true fins. At night, especially when thus in motion, it
appeared most brilliantly phosphorescent; the light flashing progressively but very rapidly
along the body, especially from all the branchial tufts and the edges of thé veil and crest. At
other times it remained quiescently adhering to the sides of the glass, or moving slowly up
and down, as if in search of food; seeming to use the veil as a feeler, but with the tentacles
reflected. Sometimes it crawled in the usual inverted position along the surface of the water.”
“ Its mode of swimming perfectly resembles that of the larva of the gnat so common in
our English cisterns of rain-water/’f This is the only account of the phosphorescence of
the Nudibranchs that we recollect to have seen.
The Nudibranchiate Mollusca are very sensitive to external influences, shrinking quickly
from contact, and withdrawing their organs on the least sense of danger. When crawling on
sea-weeds or corallines, they often detach themselves on being disturbed, and drop to the
bottom of the water. The Polides, when alarmed or irritated, erect their papillae, and
sometimes agitate them in a convulsed manner, directing their apices to any source of
annoyance; each papilla being endowed with a motion independent of the others. On such
occasions urticating filaments-are probably ejected from the tips of these organs. We once'
had an opportunity of observing fluid emitted from the papillae of Pólispicta. While watching
this species, with the aid of a powerful lens, as it was moving about in a small vessel of water,
the animal became suddenly alarmed, raising and twitching its papillae, which at the same
instant .gave out from their apices minute streams of a milk-white fluid; these curling upwards
were dissipated in the surrounding medium, and there can be little doubt contained urticating
bodies, which the papillae always eject on slight pressure. The papillae of Polis, Doto, Antiopa,
and some other allied genera, are very slightly attached to the back, and the animals appear
to have the power of casting them off voluntarily, in the same manner as a crab throws off its
claws, or a star-fish its arms. We have frequently found an Polis or an Antiopa that had been
injured in capture, or placed in sea-water that was a little impure, throw off the whole of its
branchiae in a very short time. It is curious to see the papillae on such> occasions swimming
through the water like independent worms, propelled by the vibratile cilia, and occasionally
by a convulsive motion of the muscles, which do not lose their vital power quite immediately.
The organs thus cast, off are quickly reproduced when the animal is in a healthy state; and
what seems strange is that, in the mean time, it does not appear to suffer any inconvenience
from the loss of these, as might have been supposed, vital organs. Even when they are all
* This genus we take to be synonymous with Plocamopherus of Ruppell.
t ‘Ann. Nat. Hist./ v. 11, p. 311.
removed the animal will crawl about in perfect unconcern; and in this state they have been
observed to copulate. The power of renewing lost or injured parts is enjoyed by these little
Mollusks in common with the rest of the class, and it is interesting to observe the progress of
their growth, which may readily be done when the animals are kept in a glass vessel. In an
Polis so confined, and in a great measure deprived of food, we have seen the papillae reappear
and attain a considerable size in three or four days. At first they resemble tubercles, without
central gland, which, however, soon makes its appearance, and assumes its normal character.
Their tenacity of life when kept in confinement varies much in the different species, but
is greater than in many other marine animals. Any impurity in the water, or too great change
of temperature, affects them very sensibly, so that it is difficult to keep them alive in warm
weather, particularly those from deep water. The littoral species can sustain a greater change
of temperature, and may be kept alive for a considerable time out of water in a moist saline
atmosphere, but they die almost immediately when deprived of moisture. Their power of
enduring abstinence is remarkable. We have kept them for weeks, and even months, without
food, and have observed little diminution of their vital energy. In such cases they generally
lose a good deal of colour and become very transparent.
But, though so patient and long-suffering in the endurance of hunger, these little animals
are very voracious. The greater number of them are carnivorous; living principally upon
zoophytes and sponges. The Alcyonium digitatum is a favorite food with the Dritonies; and
the Actinias and Lucenarite often fall a prey to the attacks of the Polides. These latter, indeed,
do not scruple occasionally to devour the weaker among their own brethren, as we have
elsewhere recorded. Sir J. G. Dalyell states that his Polis histrix {Drummondi) “fed voraciously
on mussel, and on the common periwinkle, whereof large portions were swallowed entire;”
and he thinks that Goniodoris nodosa feeds upon Ascidia papilla (Cynthia rustica), to which he
attributes the reddish colour observed in the viscera. This colour, however, is caused by the
liver and ovary. We have taken from the stomach of Polis papillosa minute specimens of the
common mussel, and a small Terebra from that of Tethys. The more common food of the
tribe, however, is the flexible zoophytes. Until lately the Dorides have been considered
vegetable feeders, but this would appear not to be the case. Doris tuberculata feeds upon the
common encrusting sponge (Halichondria panicea), and sponges and zoophytes seem to
constitute the food of most of the others. A few of the gregarious Nudibranchs, such as
Polycera quadrilineata, Hermcea dendritica, and Alderia modesta, which congregate on marine
algae, appear to be phytivorous; but Polis despecta, and P. exigua, though not unfrequently
gregarious on the fronds of Laminaria digitata, are only found on those parts of the plants that
are covered with the parasitic zoophytes, Laomedea geniculata and L. gelatinosa, on which they
feed and deposit their spawn.
Most of the species that are found between tide-marks make their appearance periodically,
and the common kinds are generally found in considerable numbers for a time, extending from
one to three months, after which they almost entirely disappear. This is their breeding
season, and it is generally considered that these animals live mostly beyond low-water mark
for a great part of the year and come into shallower water to spawn, as is the case with several
tribes of marine animals. This opinion, however, does not accord with what is known of the
habits of other Mollusks. It is not likely that creatures so defenceless and limited in locomotive