BRITISH NUDIBKANCHIATE MOLLUSCA. 5 



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 Verany, whose Catalogue of the Mollusca inhabiting the Gulph of Genoa, f includes 

 forty-eight species of Nudibrancldata. The Sicilian species described by Philippi are twenty- 

 six.]: 



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.] 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 Eolidiclce, 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 

 (Jntiopa 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 



* 'Index Molluscorum Scandinavise/ f ' Catalogo degli Animali invertebrati, &c/ 



J 'Enumeratio Molluscorum Sicilies/ 



§ 'Annales 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. 



f Vol. 19, p. 274 (1843). 



