THE BAY OF BISCAY. 177 



he had discovered an Annelid, the Amphicora, which 

 carried at the end of its tail two eyes, which were 

 perfectly similar to those which were upon its head. 

 How, it was asked, were we to admit such a trans- 

 position of the senses ? how was it to be supposed 

 that eyes could exist at so great a distance from the 

 brain, and without having any probable connection 

 with it? The question was thus made a general 

 one, and consequently acquired a very high degree 

 of physiological importance. It was no longer suffi- 

 cient to ascertain whether eyes did or did not exist, 

 but it was now further necessary to decide if any one 

 portion of the nervous system, excepting the brain, 

 could become the seat of sensorial perception. 



If by the word eye we must understand an Organ 

 which is always the same, and everywhere similar to 

 that which we find in Man or Birds, Annelids, Ne- 

 mertes, Planarias, and Medusas are certainly blind 

 animals, but, like every organic apparatus, the visual 

 organ may be simplified and degraded, without, on 

 that account, changing its nature. Even in this state 

 of degradation it maintains its fundamental parts, and 

 these parts are generally easy of recognition. 



Although destined to fulfil an entirely physiological 

 function, the eye is a true physical apparatus. It 

 always consists of a camera obscura, in which a con- 

 verging lens concentrates the light, and throws the 

 image of external objects on a screen which is placed 

 in its focus. But here the lens instead of being 

 formed of inert matter is organised, and is known as 

 the crystalline lens. The screen is also living, and 

 bears the name of the retina, and it is through the 



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