156 Miiller on the Eye in Murex Tritonis. 



by the substance of the feeler. The eye itself is easily sepa- 

 rable from the surrounding substance, and is then seen as a 

 blackish sphere, with its greatest diameter in the longitudinal 

 direction. A thin transparent lamella, continuous with the 

 substance of the feeler, is expanded in front of the globe of the 

 eye. This cornea, as it may be considered, is separated from 

 the globe by a space extending over its anterior third, which 

 in the recent state is probably occupied by a fluid (aqueous 

 humour). 



The posterior part of the globe, embedded in the substance 

 of the feeler, is formed by a greyish-black membrane (choroid), 

 which at its anterior part forms a narrow circular belt of a 

 darker colour (iris), perforated in its centre by a circular 

 pupil. The external margin of the cornea reaches somewhat 

 farther back than the outer edge of the iris. 



The optic nerve, which is a branch of the nerve running 

 in the axis of the feeler, perforates the posterior part of the 

 cup formed by the choroid, and probably expands on its inner 

 surface into a retina, of which some imperfect traces were 

 visible. The inner surface of the choroid is perfectly black ; 

 its cavity is almost completely occupied by a firm, round, 

 amber-coloured mass, similar to those found in the eyes of 

 spiders, and representing either a crystalline lens or vitreous 

 humour. 



As the most essential parts of an eye are here present, 

 and of comparatively large size, we are warranted in supposing 

 that there must be a corresponding power of vision. Experi- 

 mental observations on this point are the more desirable, as 

 in Helix and Cyclostoma, where there is a similar organization, 

 the animals appear not to see, or at least not distinguish 

 objects. 



