196 Messrs. Hancock and Embleton on the Anatomy o/Eolis. 



pedicle, the optic nerve, PI. V. figs. 1 & 2, no. 16, which comes 

 off from the upper surface near the middle of the external border 

 of the median cerebral ganglion, close to its connection with the 

 lateral one. The nerve is directed forwards, outwards and up- 

 wards, and varies somewhat in length in different species ; it is 

 covered by a very delicate transparent sheath : the eye itself, 

 PI. V. fig. 3, has a wide external envelope — a delicate transpa- 

 rent capsule, a, continuous with the sheath of the nerve. This 

 envelope holds the place of the cornea and sclerotica of more 

 highly organized eyes. Within it is contained an irregularly- 

 shaped cup, b, of black pigmentary matter, which embraces the 

 posterior half of a spherical, colom-less, highly refractive crystal- 

 line lens, c. 



The anterior border of this pigmentary or choroid coat appears 

 to be free, and is irregularly crenate. Over the front of the lens, 

 and separated from it by a narrow interval, is a transparent 

 tunic, d, which is most aptly compared to the anterior capsule of 

 the lens of the higher animals, though some may deem it the 

 homologue of the cornea. The back part of the choroid coat 

 seems to be pierced by the optic nerve, but from the minuteness 

 of the organ and the opacity of the choroid, we have not been 

 able to determine the exact relation of the retina to the pigmen- 

 tary layer, nor the existence of a vitreous body. 



The degree of vision enjoyed by these animals must be slight. 

 They can distinguish light from darkness, and can probably ap- 

 preciate imperfectly different degrees of light, and as the eyes are 

 placed under the skin of the head, their perception of objects 

 must be exceedingly faint and indistinct. 



The auditory apparatus consists of a minute, elliptical, delicate, 

 and transparent capsule, PI. V. figs. 1 & 2. no. 17, less than the 

 eye, directly behind which it is situated; it appears sessile upon the 

 external border of the median cerebral ganglion, but there are 

 faint indications of a pedicle or a nerve that enters the capsule at 

 the front. The long diameter of the capsule lies in the antero- 

 posterior direction ; within this capsule, figs. 4 & 5 a, is another, 

 b, still more delicate and much smaller. This latter contains 

 numerous very minute, oval corpuscles or otolithes, fig. 4c, smooth, 

 transparent, and highly refractive of light. In the centre of each 

 an obscure dot, fig. 6, occurs, which, when highly magnified, ex- 

 hibits a distinct appearance of nucleus and nucleolus. They are 

 seen as we have described them in E. papillosa and E. coronata ; 

 but in E. aurantiaca and E. olivacea, in E. picta and E. exigua, 

 there is only one large spherical otolithe, fig. 5 b, which presents 

 also indications on its surface of nucleus and nucleolus. 



These capsules are specimens of the auditory organ in perhaps 

 its simplest form, and as such are adapted for the most limited 



