506 Mr. Brayley on the ocular points of the Helicidce^ 



tentacules ties irritables presentent une large surface ou un filet 

 si delie qu'ils doivent percevoir les plus legeres impressions, mais 

 toujours diriges en avant ils ne pourroient avertir Panimal du 

 danger quMl coure par derriere, ou pour cette raison les yeux sont 

 places. II n'eut pas ete prudent d'ailleurs de mettre les yeux aux 

 sommets des tentacules chez des mollusques, beaucoup plus ex- 

 poses encore que les terrestres aux mutilations accidentelles." 



Having now shewn the general state of opinion on this subject, 

 by the foregoing quotations from the works of some of the most 

 eminent naturalists, I shall hasten to conclude this article, which 

 may perhaps already have appeared tedious to some of your 

 readers, by the inferences I am disposed to draw from the whole 

 of the evidence before us. 



The general remark of Aristotle in the passage quoted from 

 lib. iv. cap. viii. of his History of Animals, respecting the senses 

 of sight and hearing in the Testacea^ and the account which is 

 annexed io it of some of the habits of certain bivalves, must not 

 be considered, I think, as in any degree contradicting his pre- 

 vious statement, that those animals are destitute of Eyes. For, 

 although the actions of the Bivalves alluded to might appear to 

 furnish some ground for such contradiction, (did we not certainly 

 know that the classes of MoUusca which construct Bivalve shells 

 are absolutely devoid of the sense of vision,) yet Aristotle refrains 

 from drawing such an inference ; but seems rather to bring for- 

 ward the instances as remarkable facts, connected with the sub- 

 jects he is investigating, though not affording positive informa- 

 tion concerning them. 



I have already observed that the Gasteropoda appear io be the 

 only class of MoUusca from which even a hypothetical contra- 

 diction of the Stagirite's assertion can be derived ; — that they are 

 the only true MoUusca stated to enjoy the sense of vision. But 

 what do we find to be the state of science respecting what are 

 deemed their organs of sight? Why, that some naturalists, 

 without giving any reasons for their belief, affirm them to be 

 Eyes ; that some merely suspect them to be Eyes ; that others, 

 again, appear to suspect they are not Eyes : but that none have 

 advanced any direct evidence on either side; — if we except Mr. 



