situated. But the characteristic peculiarity of these mollusks is the appendages that constitute
their breathing organs, placed upon the back, always symmetrically, in plumes, tufts, or
papillae, either forming a circle on the central line, or arranged in rows upon the sides.
Unfortunately, the Nudibranchiata are as perishable as they are beautiful, it being
impossible to preserve them after death in their original forms and colours. From this
circumstance it is that they are so little known to the generality of persons, and that specimens
are seldom to be found in museums. The shapeless and colourless mass which most of them
present when preserved in spirits, is, indeed, a very poor representation of the living animal :
yet even in this state, imperfect as it is, they are useful for the examination of the zoologist,
as the characters may generally be observed by which the species are distinguished ; not to
mention the value of such specimens for the purpose of dissection. I t is much to be regretted,
therefore, that these animals are not more frequently preserved, and that scientific travellers
of our own nation have so seldom paid attention to the foreign species, either by preserving
specimens for examination, or by making drawings of the living animals on the spot ; both of
which are necessary for a proper knowledge of the genera and species.
None of the Nudibranchiate Mollusca appear to have been known to the ancients, and
even up to the time of Linnæus, they remained, with one or two rare exceptions, entirely
unnoticed. In the 12th edition of his ‘ Systema Naturæ,’ only seven species were described,
scarcely any of which had come under his own observation in a living state. They were
placed by him in the class Vermes, and referred to the genera Doris, Scyllcea, and Tethys.
That excellent observer, Otho Frederic Müller, paid more attention to them : twelve species
are characterised in his ‘ Zoologiæ Danicæ Prodromus/ most of which were afterwards figured
with fuller descriptions in the ‘Zoologia Danica.’ The number of species introduced into the
latter work is fourteen. Otho Fabricius has also excellent descriptions of two or three of these
mollusks in his ‘Fauna Grcenlandica.’ Other authors contributed a little to increase the
number of species, among whom Bommé, who described several in the Flushing Transactions,
is deserving of honorable mention. But these sparing contributions—few and far between—
were not sufficient to attract the general attention of naturalists to a group of animals difficult
of observation, and whose physiology and habits were as yet entirely unknown. It was
not until the appearance of the celebrated ‘ Mémoires’ of Cuvier, in the ‘Annales du Muséum,’
that much attention was drawn to this subject. These formed a new era in their history, and
the dissections there given furnished the groundwork for those more correct views of their
affinities which that distinguished naturalist carried out in the ‘ Règne Animal/ where the
order Nudibranchiata was first instituted for their reception. Even at that time, however,
very few species were known, and it is to be regretted that Cuvier was obliged to have
recourse to specimens preserved in spirits for his descriptions. So far as their anatomy was
concerned, this disadvantage was not greatly felt, but the figures and descriptions of their
external forms were in consequence very imperfect. The position of this group in relation to
the testaceous tribes, from which they had been kept apart in the Linnean arrangement,
began now to be generally acknowledged. Their affinities were further illustrated in the
celebrated ‘ Histoire Naturelle des Animaux sans Vertèbres/ of Lamarck, and in the ‘ Manuel
de Malacologie ’ of Blainville ; each of which contributed something to the knowledge of their
physiology and relations, but not much to the number of species.
Let us now see what had been done during this time by the naturalists of our own
country. Stanch disciples of the Linnean school, the British naturalists had applied
themselves to the study of species with much more alacrity than their more speculative
brethren of the Continent, and the Fauna of the British Islands had in consequence assumed
a more full and comprehensive form. One is disappointed, therefore, to find how very little
was until lately known of the Nudibranchiate Mollusca of our own shores. The ‘British
Zoology’ of Pennant, published in 1777, contains just three species, which he calls Doris
Argo, Doris verrucosa, and Doris electrica; the two former are common and conspicuous
animals that could scarcely be overlooked by a collector; the latter is so imperfectly described
that it cannot now be identified. For more than twenty years after the publication of
Pennant’s work, no further notice was taken of this neglected tribe. In 1802, however,
.Montagu published in the ‘Linnean Transactions’ the first of his series of papers on the
marine animals of the Devonshire Coast. In these excellent papers twelve species of
Nudibranchiate Mollusca were described, all new to Britain, and, with the exception of two
or perhaps three species, then unknown to naturalists. They were all referred to the genus
Doris, which at that time was the general receptacle for most of the species of the order. In
such veneration, indeed, was the arrangement of the great Swedish naturalist then held by
English authors, that even his genera were considered sacred from the hand of innovation,
and each new form, however incongruous, was referred to some known Linnean genus.
Montagu, however, was too accurate a student of nature to avoid seeing the necessity of some
change, and in one of his later papers we find him proposing to admit the genus Tritonia of
Bose, for a part of the Dorides, but still, in deference to the naturalists of the Linnean school,
he does not venture at once on such an innovation but reserves it for further consideration.*
The species described 'by him are ;—Doris pinnatifida, D. ceerulea, D. flava, D. marginata,
D. maculata, D. longicornis, D. nodosa, D. papillosa, D. quadricornis, D. pennigera, D. pedata,
and D. bifida, none of which now belong to the restricted genus Doris, but are distributed into
seven different genera. Unfortunately, several of them have not since been met with. We
have used every exertion to ascertain the species described by Montagu, pursuing our
investigations in the localities where they were found. Some of them, however, have entirely
eluded our search, and one or two others we can only with doubt refer to species known to be
common on the Devonshire Coast, and, therefore, likely to have been met with by that
naturalist. Dr. Turton’s ‘British Fauna’ appeared in 1807, and contained nine species of
Nudibranchiata, only one of which was introduced from personal observation; three were those
of Pennant, and five of Montagu. The species introduced by Turton he calls Doris vermigera.
It was, without doubt, the common JEolis papillosa, afterwards described by Montagu in the
‘ Linnean Transactions.’
Another period of twenty years passed after the discoveries of Montagu, during which
this tribe was scarcely noticed by any British author, though in the latter part of this period,
Dr. Leach appears to have paid some attention to the subject while collecting materials for his
work on the British Mollusca,f which, owing to the distressing illness that obscured his latter
days, remained long unpublished, and has only just appeared, edited by his friend and former
pupil, Dr. J. E. Gray. Had this work appeared at the time when it was written, much
interest would have attached to it, as Dr. Leach had the merit of being the first English
* I Linn. Trans./ v. 11, p. 196. t ‘A Synopsis of the Mollusca of Great Britain/