130 



HORNS OF THE SNAIL. 



character of the apparatus which has thus been de- 

 scribed ; it is, of course, a magnified representation of 



a longitudinal section of each horn, a^ one of the 

 larger horns protruded, showing b, the eye ; c, the 

 retractor muscle ; d, the optic nerve ; e, the muscular 

 wall of the tube, composed of circular fibres ; f, the 

 ganglion from which the nerve of the eye arises ; g, is 

 a smaller horn, with its retractor muscle, c, but the 



