THE EYE OF GASTEROTODS. 191 



means obscure ; * and the giant Strombidas, which inhabit the 

 Caribbean Sea, have eyes more perfect than those of many 

 vertebrated animals. They have, according to the late Rev. 

 Lansdown Guilding, a most intelligent and indefatigable na- 

 turalist, a distinct pupil and a double iris, equalling in beauty 

 and correctness of outline those of birds and reptiles ; and he 

 discovers in the organ a vitreous and an aqueous humour, 

 and the black pigment, f Mr. Gray, a naturalist of equal 

 industry and accuracy, tells us that if they who have doubted 

 concerning the nature of these organs " had examined the 

 eyes of the marine carnivorous mollusca, Buccinum undatum 

 or Fusus despectus, and more especially some of the larger 

 Strombi, they would have found the eye as fully developed 

 as in the cuttle-fish, showing the cornea and the nearly or- 

 bicular crystalline lens almost perfectly formed, as may be 

 seen by any person simply cutting the cornea across, and 

 slightly pressing it, when the crystalline lens will pro- 

 trude." j This evidence seems conclusive ; for if the same 

 parts cannot be demonstrated in the smaller or in the ter- 

 restrial mollusca, it is surely because of the minuteness 

 of the organ and the difficulty of the dissection. But the 

 fact is, that Swammerdam has described, with great minute- 

 ness, the eye of the common snail, in which he detected 

 " five distinct and visible parts," viz. the uvea, the aqueous, 

 the crystalline, and the vitreous humours, with the arach- 

 noid tunic ; parts which, he affirms, were as " clear as the 

 sun at noon." He likewise observed that the eyes of the 

 Lymnaei were provided each with " its own proper crys- 

 talline humour." The accuracy of this description has been 

 denied, — as indeed this good man, and incomparable ana- 

 tomist, seems to have foreseen would be the case. " But 

 who can credit this ?" says he ; " for it seems indeed impro- 

 bable, that on a point not bigger than the nib of a writing- 

 pen, such exquisite art, and so many miracles, should be 

 displayed." § 



* See Blainville's anatomy of the eye of Voluta cymbium, L., in his Princ. 

 d'Anat. Comp. i. 445. 



f Zool. Journ., iv. 172. Also, Swainson on Hab. and Inst, of Anim. 

 p. 43. " In the typical Strombi, these organs are so much developed that 

 the iris is richly coloured, and the eyes of some of the larger species have 

 been described to us as particularly beautiful." — Swainson's Malacology, 

 136. 



± Edinb. Journ. Nat. Gcogr. Sc. iii. 52. 



§ Of Swammerdam's anatomy of the Snail, Cuvier says, " II en fait con- 

 naitre toutes les parties, le cceur, les visceres, le foie ; il en decrit tons les 

 muscles, et expliquc toutes les manieres dont cet animal est attache a sa co- 

 quillc. II fait connaitre ses yeux, leur cristallin, la nerf optique qui s'y rend 



