THE EYE OF PECTEN. 49 



The Eye of Pecten. 

 By 



^1^. J. Dakin, M.Sc, 



Demonstrator and Assistant Lecturer in Zoology, University 



of Belfast. 



With Plates 6 and 7, and 2 Text-figs. 



The first reference to the eyes of Pecten that I have been 

 able to find is that of Poll in 1795. Since that date more 

 than a score of investigators have studied these small organs 

 and treated in more or less greater detail the histology. 

 Bach has made new discoveries, which have in very many 

 cases been refuted by their immediate successors, to such an 

 extent, in fact, that it was almost impossible to determine 

 from the literature on the subject the truth in regard to cer- 

 tain parts. One of the last and most reliable papers was that 

 of Hesse, published in 1900 (34). He pointed out that some 

 points were still unsolved (though adding one or two dis- 

 coveries himself), and that the success of the methylene-blue 

 method, if attained, would possibly elucidate all. 



In 1904 a paper appeared by Miss Hyde (39), embodying 

 the results of a successful employment (according to the 

 author) of the methylene-blue methods for nerve-endings in 

 the retina, but these results were certainly not those expected 

 by Hesse nor probably by other authors, for they stand in 

 striking opposition to the views previously held. Whilst 

 working at a memoir on Pecten in 1907, I came to the con- 

 clusion that this, the latest investigation of the Pecten eye, 

 differed greatly from the preceding ones, and that only one 



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