of Calliopsea and on four new species of Eolis. 237 



veral species of Conchifera*. We have lately had the pleasure of 

 recognising the same organs in the Nudibranchia ; they consist 

 of two transparent vesicles connected with the two superior lobes 

 of the brain by short nerves. These vesicles are filled with small 

 concrete bodies or otolites^ varying in number according to the 

 species, and vibrating, when in a living state, with a continuous 

 oscillatory motion. 



In Eolis papulosa the otolites exceed eighty ; they are elliptical 

 and very minute ; while in E. olivacea and E. pallida there is only 

 one large globular otolite in each capsule. We have observed 

 these organs in species of the genera Eolis, Tritonia, Meliboea, 

 Poli/cera and Doris ; in all of which we find them similarly situ- 

 ated and undergoing only very slight modifications. 



The eyes are placed immediately before the auditory capsules, 

 and the nerve that supplies the former arises from the same por- 

 tion of the large ganglion above the oesophagus to which the lat- 

 ter is affixed. The eye is much more completely organized than 

 has been supposed ; it is formed of a well-defined cup of black 

 pigment, through which in all probability the retina is dispersed. 

 Before this cup is placed a large spherical crystalline lens, having 

 a well-arched cornea in front. The whole is enveloped in a thin 

 transparent vesicle attached to the ganglion by a pedicle, through 

 which the optic nerve passes into the base of the cup. 



The organs of smelhng remain yet to be ascertained. De Blain- 

 ville has suggested that this function may be performed by the 

 dorsal tentacula, and a careful examination of the structure of 

 these compared with that of the olfactory organs in other animals 

 has led us to adopt the same opinion. The simplest form in 

 which the organs of smelling are known to^ exist, is in fishes and 

 in some of the Crustacea. If we examine^ this organ in a fish, 

 the common herring for instance, we shall find it to consist of a 

 delicately lamellated expansion contained within a cavity, open 

 externally, but closed on its internal surface, and communicating 

 with the brain by a nerve having a small ganglion at its base. 

 Now if this lamellated portion were bent intp a cylindrical form 

 and raised upon a pedicel capable of being ^otruded from the 

 cavity, we should have a structure exactly simriar to ^the dorsal 

 tentacula in Doris. It is easy to tracfe the modmcation^ of this 

 form through the other genera of the order, in most of which 

 the plicated structure is more or less visible, the organ being in 

 some carefully protected by a sheath. In all, the tentacula are 

 furnished with a nerve which generally has a small ganglion at 

 its base, as in the olfactory nerve in fishes. On examining the 

 tentacula under a microscope, the whole sm'face is found to be 

 very strongly ciliated ; more strongly even than in the branchial 

 * See this Journal, vol.ix. p. 501.— Ed. 



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