508 Mr. Brayley on the ocular points of the HelicidcB^ 



M. de Ferussac's acute remarks on the diflference of position in 

 these organs, as borne by the terrestrial and the fluviatile PuU 

 monifera^ will apply to them with equal truth, when they are 

 considered, not as organs of sight, but as the organs of a delicate 

 sense of feeling^ distinct from the ordinary touch adapted to the 

 examination of concrete substances. And, with this construction, 

 his reasoning on the subject disarms the objection to M. Gaspard's 

 statement, which Mr. Guilding derives from the situation of the 

 black points " at the very base of the feelers of Limncea^ and 

 Helicina;^^ with regard, at least, to the former genus, which is 

 known to be an inhabitant of the waters. The marine Mollusca 

 alluded to by Mr. G. are doubtless Cephalopoda^ and as such the 

 perfect structure of their eyes has no bearing on the subject 

 before us. 



As Aristotle expressly classes the Oc^ax»^sf/^ta as exsanguineous 

 animals, (quasi animals devoid of red blood,) it is not probable 

 that he confounded with them the testaceous Jnnelides; but 

 even if this was the case, his assertion will still hold good, for the 

 latter are admitted to be devoid of sight ; and the other groups 

 of the same class have only the equivocal black points of the 

 Gasteropoda. 



In concluding this hasty sketch of so interesting a subject, I 

 must unaiFectedly acknowledge my sense of its imperfect and un- 

 satisfactory nature ; and this acknowledgment demands a state- 

 ment of my reasons, for presenting it to the readers of this 

 Journal. Those reasons were as follows : finding so important a 

 part of the history of the Mollusca enveloped in an obscurity, 

 which was unlikely, it appeared, soon to be dispelled, I consi- 

 dered, that though I should be unable, from other and pressing 

 avocations, to give the matter the full elucidation it deserved, 

 yet, that I might, by exhibiting the present state of science re- 

 garding it, contribute in some small degree to the advancement of 



Eyes to enjoy the sense of vision ? To beings occupying so low a rank in 

 tlie Animal Kingdom as the Mollusca and the Jnnelides, nothing more, prob- 

 ably, is requisite, than the sense of the presence of sound and of light, for their 

 security or their enjoyment; which they would receive by these means aaj 

 effectually, as if they were enabled to hear and to see. 



