Professor MuHer's Recent Discoveries on the 



Art. III. — Notice of Professor Mullers Recent Discoveries on 

 the Structure of the Eyes of the Gasteropodous Mollusca. 

 By the Editor. ( With a plate.) 



The structure of the eyes of insects* and mollusca, has 

 recently been the subject of careful investigation with con- 

 tinental anatomists. The labours of Professor Muller, of Bonn, 

 have been particularly successful in this branch of anatomy, and 

 we conceive, are entitled to especial attention. And having in 

 our possession a minute and accurate description of the eye of 

 one of the cephalopoda^ the highest family of the mollusca, by 

 our friend Mr Jones, we think that there cannot be a more 

 fitting place than this, for the introduction of a notice of 

 Muller's account of the anatomy of the eye of the ffasterqpoda, 

 the second division of the same great order. 



In the snails, as in most other gasteropoda, the eyes are found 

 at the extremities of the largest tentacula. These tentacula, 

 when extended, may be represented as formed of two portions, 

 one basilar, and the other terminal. During the retraction of 

 the tentaculum, the latter portion entering the other, becomes 

 internal, — a change which is effected by the contraction of the 

 muscular fibres which surround the walls. 



Plate VIII. Fig. 1. represents the interior of the tentaculum 

 of the snail (Helix pomatia,) in the state of extension, a, The 

 nerve of the tentaculum ; /;, the fleshy cylinder ; c, the external 

 skin of the tentaculum, which is joined at d with the fleshy 

 cylinder ; c, the eye, situated a little laterally. 



Fig. 2. The tentaculum on the point of being drawn inwards. 

 Fig. 3. The tentaculum much drawn inwards, a, The part of 

 the external membrane of the tentaculum still projecting ; 

 6, that part of the membrane which is drawn in and reverted ; 

 <?, the black fleshy cylinder, hollow in its upper part, which is 

 joined at d with the outer membrane of the tentaculum ; at this 

 place, the eye is seen by its transparency : e, the nerve of the 

 tentaculum entering sidewise into the upper hollow part of the 

 fleshy cylinder. 



If the skin of the tentaculum, making the continuation of the 

 fleshy cylinder, be opened, (fig. 4.) we see more distinctly the 

 outer skin of the tentaculum and the cylinder joined together. At 

 the extremity of the black fleshy cylinder is a white hemispherical 

 body, which carries the eye on one side. This hemispherical 

 body is the last part of the tentaculum retracted, at the margin 

 of which the skin is connected with the black fleshy cylinder. 



If the black cylinder (fig. 5.) be dissected out with caution, 

 we see the great nerve of the tentaculum crossing this hollow 

 sheath in many convolutions, and then entering, not into the 



* An account of Muller's investigations into the structure of the eyes of insects, 

 may be found in No. XVIII. of Loudon's Mag. of Nat. Hist. 



