o/ Calliopsea and on four new species o/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 ^\dth 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. oUvacea 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, 

 Polycera 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 abo^e the oesophagus to which the lat- 

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

 has been supposed ; it is fomied 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 smelling 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 structm-e of 

 these compared with that of the ohactory organs in other animals 

 has led us to adopt the same opinion. The simplest fonn 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 into a cylindi-ical form 

 and raised upon a pedicel capable of being protruded from the 

 canty, we should have a structm-e exactly similar to the dorsal 

 tentacula in Doris. It is easy to trace the modifications of this 

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

 the plicated structm-e is more or less visible, the organ being in 

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

 furnished vnih a nerve which generally has a small ganglion at 

 its base, as in the olfactoi-y nen^e 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. 



