Description of the Eye of the Cuttle Fish. 285 



The next higher family of Mollusca is the Cephalopoda, the 

 greater complexity and peculiarities of whose eye are in perfect 

 accordance with the remarkable anomalies which distinguish this 

 from all other animals. The anatomist who is acquainted with 

 the nature of our previous knowledge of the structure of this 

 organ, will be able to appreciate the corrections which Mr 

 Jones has been enabled to deduce; and the general reader will 

 be struck by the comparison of the preceding descriptions with 

 the following notice. 



To compare the functions of these organs is impracticable in 

 the present state of our knowledge, 

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ART. IV. — Description of the Eye of the Cuttle Fish, (Loligo 

 sagittata.) By T.W.Jones. 



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The eye is a perfect optical mstrument, composed of mem- 

 branes and humours of different degrees of density, which 

 transmit and converge the rays of light; so that they may 

 exactly impinge on the sensitive part of the organ. But as 

 water has a density different from air, and as diff'erence in 

 density has an influence on the mode of transmission of light, it 

 follows that the eye, which can see in air, shall not see in water. 

 This difference has been provided for. Does an animal live on 

 the surface of the ground ?— the cornea is moderately projecting, 

 and the crystalline lens rather flat. Does the animal soar to 

 great heights? — the cornea becomes more projecting, and tliq 

 crystalline lens flatter. Does the animal live in water P-ttj^^^- 

 cornea is quite flat, and the crystalline lens spherical. (., (Ijrj'jo 



Such are the modifications, (founded on optical principles,); qf- 

 the eye in diff*erent animals ; but if we meet with one, the eyg); 

 of which, (at first sight very large, and highly organized, an^,;. 

 the-refore, apparently well adapted for vision,) presents certain 

 structures, incompatible with the usual function of an eye, Wj^ 

 are struck with the anomaly, and are induced to exclaim,—:, 

 " What can be the use of this organ, in some respects so highly 

 organized, and in others so imperfectly adapted for vision ?" 



On the structure of the eye of the cuttle fish, which possesses 

 the peculiarities I have described, I propose to make some 

 remarks, and endeavour to correct the confusion in which the 

 anatomy of this organ is involved, by the inaccurate and vague : 

 descriptions given by those who have treated of it. * 



In the Loligo sagittata, the opening of the eyelids is sufficiently - 

 large to allow the crystalline lens to project. j|^|^l^he,piargin of 



* Whetlier tlie doctrine of unity of organization can, or can not, be extended to 

 the invertebrata, it is difficult at present to decide. Until, however, it . is sati^ac- 

 torily proved, either one way or the other, we must speak of thporgans of the 

 invertebrata always with a reference to those of the vertebrata. , : ; < 



