178 RAMBLES OF A NATURALIST. 



latter that the impression received from images is 

 transmitted to the brain. However varied may be 

 the degree of complication in an eye, its fundamental 

 parts always consist of a crystalline lens and a retina. 

 We are therefore on the other hand bound to consi- 

 der as a true eye every organ which possesses these 

 characteristic elements ; for it could not fulfil any 

 other functions but those of which we have spoken. 

 To decide this general question advanced by Ehren- 

 berg, and to ascertain whether in fact the visual 

 organ can be thus transposed, or, in other words, 

 whether it can exist elsewhere than in the head, we 

 must necessarily find in the Amphicora, or in every 

 other animal presenting analogous facts, the crystal- 

 line lens and retina of the eyes.* 



In this respect my investigations continued for a 

 long time to be unsuccessful. On the coasts of the 

 Channel and of Sicily, I had found many Annelids 

 allied to the Amphicora, and bearing on the posterior 

 extremity of their bodies the coloured points in 

 question. In some of the species that I had disco- 

 vered, these coloured points were moreover strangely 

 multiplied. There were several of them on the head, 

 four at the extremity of the tail, and two on each 

 ring of the body. This multiplication seemed to me 

 to present in itself a very serious objection to the 

 views of Ehrenberg. How was it possible to believe 

 in such a profusion of visual organs ? Yet the study 

 of the living animals seemed to confirm this determi- 

 nation. I saw the tail fulfilling all the functions of 



* The term crystalline lens is here used to express generally the 

 whole refractive apparatus of the eye. 



