naturalist to adopt the more modern views of the French school. At present it comes behind
the knowledge of the day, and is chiefly valuable as a document in the history of the science.
The Nudibranchs described in it amount to twelve, of which two or three are varieties, and
the rest have now been described by other authors. The first arrangement of the British
species into modern genera was given by Dr. Fleming in his ‘Philosophy of Zoology/ and
subsequently in his ‘History of British Animals/ which appeared in 1828. This work
contains twenty species of Nudibranchiata, six of which were introduced into our fauna for the
first time; viz.—Doris Icevis, Doris nigricans, Tritonia Hombergii, IHtonia arborescens, Eolida
plumosa, and Eolida purpurascens. In 1838 Dr. Johnston published his excellent Monograph
of the ‘ Scottish Mollusca Nudibranchia’ in the first volume of the ‘Annals of Natural History.’
I t comprises an anatomical and physiological account of the animals contained in the order,.
and goes far to extricate the synonyms from the obscurity in which they had been involved.
The species new to Britain introduced by Dr. Johnston, either in this treatise, or previously
in Loudon’s ‘Magazine of Natural History/ amount to eight: they are Doris obvelata
(Johnstoni, A. and H.), Doris pilosa, Tritonia plebeia, Triopa claviger, Triopa nothus, Melibcea
pinnatijida {Jragilis, For.), Eolidia Cuvieri, and Eolidia rufibranchialis. From this period much
more attention has been paid to the Nudibranchiate Mollusca by British naturalists, and new
genera and species have been discovered in increased ratio. This has resulted partly from
the more extensive explorations of our coasts by means of the dredge that have been so
successfully carried on of late years, but principally from the more careful mode of investigating
nature that naturalists now find it necessary to adopt. The researches of Professor Edward
Forbes have added considerably to our knowledge of the Nudibranchiata; eight or ten new
species have been contributed to the British list by his means. To Mr. Thompson, of Belfast,
science is also indebted for much information and several new species in this department,
obtained during his extensive investigations into the natural history of Ireland, now,
unfortunately, put a period to by his untimely death. Shortly after the publication of
Dr. Johnston’s memoir, the authors of the present work first began to turn their attention to
the Nudibranchiata. Since that time they have had the good fortune to introduce into our
fauna upwards of sixty species, principally the result of their own personal researches; for
the knowledge of a few of them, however, they are indebted to friends, particularly to
Mr. W. P. Cocks, of Falmouth, to the Rev. D. Landsborough, jun., of Saltcoats, and to Mr.
Barlee. The number of British species now described in this work amounts to one
hundred.*
It will not be necessary here to enumerate the additions that- have been made to this
department of the European fauna during the last half century. Suffice it to say that of late
years much attention has been paid to the Nudibranchiata by continental naturalists, and
several new species have been described. Among the authors treating of the subject may
be mentioned, Risso, D’Orbigny, Cantraine, Quatrefages, Sars, Loven, Delle Chiaje, Philippi,
* The second volume of Sir J. G. Dalyell’s ‘ Powers of the Creator displayed in the Creation/
published since the above was written, contains descriptions of twenty «five species of Nudibranchiate
Mollusca, most of which are familiar to us. Two or three species may possibly be new, but the
descriptions are too imperfect to found an opinion upon, especially as they come very near to others
already known. Some interesting remarks on the habits and embryology of these animals will be
found in the work.
and Verany. No account, however, of the Nudibranchiate Mollusca of any one country has
yet been published sufficiently complete to form the basis of a comparison with our own. The
best are those of Loven,* who gives thirty-seven species as members of the Scandinavian fauna,
and of Yerany, whose Catalogue of the Mollusca inhabiting the Gulph of Genoa,! includes
forty-eight species of Nudibranchiata. The Sicilian species described by Philippi are twenty-
six, f
But it is not in a numerical point of view alone that our knowledge of this interesting
tribe of animals has increased; their anatomy and physiology, their habits and alliances, have
lately been studied with care and attention, and many curious facts concerning them have
been ascertained. In 1841, the celebrated Norwegian naturalist, M. Sars, announced the
discovery that these little creatures undergo a metamorphosis, having on their extrusion from
the egg a very different form and character from those which they are afterwards destined to
assume. In this first stage of their existence they have the appearance of small animalcules,
swimming freely through the water by means of two ciliated lobes, and have their body
covered by a nautiloid shell furnished with an operculum. Up to that time nothing
approaching to a distinct metamorphosis had been known to exist in any of the true
Mollusca: the announcement, therefore, did not fail to excite a considerable degree of interest.
The investigation of this curious fact was pursued and extended by M.f Loven and other
naturalists, the result of which showed that this peculiar mode of development was not
confined to the Nudibranchs alone, but was common to many of the allied families; the
metamorphosis, however, is most striking in those genera^ which, like the former, do not bear
a shell in their adult state.
Professor Milne Edwards was the first to describe^ a curious conformation of the digestive
organs in the family of the Eolididce, the true signification and uses of which have since been
the subject of much controversy. Having observed in a small Calliopaa, found at Nice, a
system of branched canals connected with the stomach, and extending to the papillae and
other parts of the external surface, he thought he saw in this arrangement a blending of the
functions of digestion with those of the vascular system, which he in consequence called
gastro-vascular. This apparatus he compares to the system of vessels radiating from the
stomach of the Medusida on the one hand, and to the caeca connected with the digestive
organs of the Nymphons among the Crustacea, on the other.
During the same year (1842) M. delle Chiaje had published a figure of his Eolis cristata
(.Antiopa cristata, A. and H ), in which a similar apparatus of branching vessels connected
with the stomach is represented, but without any letter-press description. ||
The idea of the existence of a gastro-vascular system in the Nudibranchiata was promptly
taken up by M. de Quatrefages, who in the autumn of that year made a communication on
the subject to the French Academy of Sciences. The animal on which his investigations were
founded, he conceived to belong to a new genus, the anatomy of which was subsequently
given at large in the ‘Annales des Sciences Naturelles.’^f This Mollusk he called Eolidina
* 1 Index Molluscorum Scandinavise.’ + ‘ Catalogo degli Animali invertebrati, &c.’
J ‘ Enumeratio Molluscorum Sicilise.’
§ ‘ Anuales des Sciences Naturelles/ 2d series, v. 18, p. 330.
|| The text to this plate was published in 1844, where the whole is considered a ramified liver.
H Vol. 19, p. 274 (1843).