482 THE SENSORIAL FUNCTIONS. 



the globe; and Muller also discovered at the 

 anterior part, another transparent body, having 

 the shape of a lens.* A structure very similar 

 to this was found to exist in the eye of the 3Iurex 

 tritonisy with the addition of a distinct iris, per- 

 forated so as to form a pupil ; a part which ha4 

 also been observed, together with a crystalline 

 lens of very large size, in the Voluta cymbium^ 

 by De Blainville-t Thus the visual organs of 

 these Gasteropoda appear to possess every re- 

 quisite for distinct vision, properly so called. 

 Experiments are said to have been recently made, 

 both by Leuchs, and by Steifensand,| in which 

 a snail was repeatedly observed to avoid a small 

 object presented near the tentaculum ; thus 

 affording evidence of its possessing this sense. 



The accurate investigation of the anatomy of 

 the eyes of insects presents considerable diffi- 

 culty, both from the minuteness of their parts 

 and from the complication of their structure ; so| 

 that notwithstanding the light which has recently 

 been thrown on this interesting subject by the 

 patient and laborious researches of entomologists, 

 great obscurity still prevails with regard to the^ 



* Muller thus confirms the accuracy of Swammerdam's account 

 of the anatomy of the eye of the snail, which had been contested 

 by Sir E. Home (Phil. Trans. 1824, p. 4) and other writers. 



t Principes d' Anatomic Comparee, i, 445. 



X Quoted by Muller ; ibid, p. 16. These results also corro- 

 borate the testimony of Swammerdam, who states that he had 

 obtained proofs that the snail could see by means of these 

 organs. 



