Mr. Brayley on the ocular points of the Helicidce. 497 



Art. LVII. On certain Organs of the Helicidas usually 

 regarded as their Eyes : with a summary of evidence 

 in support of Aristotle^s assertion that the Testa- 

 ceous Mollusca are devoid of Visual Organs, By 

 E. W. Brayley, 7MW. A.L.S, 



[In a Letter addressed to G. B. Sowerby, Esq. F.L.S.,&c.] 



My dear Sir, 



The Rev. L. Guilding in a note to his amended generic character 

 of the genus Succinea, forming a part of his Mollusca Caribbceanay 

 inserted in the present number of the Zoological Journal, p. 442, 

 expresses his opinion, that notwithstanding the curious remarks 

 upon the subject of M. Gaspard,* '^ we may persist in calling the 

 spots on the superior tentacula [of the animals constituting that 

 genus] the eyes ; though they are without doubt very imperfectly 

 developed." " These organs," he adds, " situated at the very 

 base of the feelers of LimncBa^ Helicina, and other genera, 

 cannot surely be considered as ' organs of touch.' In some marine 

 Mollusca their structure is much more perfect." 



It occurred to me on reading this note, that an account of Mr. 

 Bauer's microscopical examination of the larger tentacula of the 

 Garden Snail, vrhich adds much weight to M. Gaspard's state- 

 ment derived chiefly from observation of the habits of the Helices, 

 vrould form an appropriate notice for the Journal ; and having 

 been led to a cursory review of the opinions held by Naturalists 

 respecting the nature of the organs in question, as possessed by 

 certain groups of the Gasteropoda in general, in consequence 

 of meeting with a passage bearing on the subject in the Historia 

 Animalium of Aristotle ; I beg to submit the results of my in- 

 quiry, through your hands, to the readers of the work. They 

 may, perhaps, stimulate some student of practical Zoology, who 

 is cohveniently situated for the investigation, to elucidate some 

 points in the physiology of the Mollusca^ to which, although of 

 much interest, but little attention has confessedly been directed. 



* See Zool. Journ. Vol. I. p. 179. 

 Vol. II. 2 I 



