108 W. J. DAKIN. 



are very different : there is a retinulate retina of one layer 

 of recipient cells which are segregated in groups of fives, 

 and the dioptric part is again represented by a corneal lens. 



It will be seen, therefore, that no eye outside the Lamelli- 

 brancli group presents anything but isolated features of 

 resemblance, and the only common structures appear to be 

 the general occurrence of rods with axial neurofibrillae or 

 visual cells with a margin of cilia-like processes arranged 

 like the teeth of a very fine comb, and these margins may 

 form rhabdomes. 



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