No. 2.] 



EYES OF POLYCH^TOUS ANNELIDS. 



179 



spheroidal mass near the brain, and scarcely separated from the 

 cuticle by the intervening epidermal cornea. The retina is a 

 single layer of pigmented cells, each having a clear rod as repre- 

 sented in the accompanying dia- __ 

 gram. The end of the rod is ^ 

 continuous with the lens, and there ^ 

 is some reason to assume it con- ^3 

 tinued into the lens as an element ^^ 

 of it. 



The above account of the eyes 

 of Nereis differs considerably from 

 that given by Graber (2), or from 

 that of Carriere (3), the only de- 

 tailed descriptions known to me. 



In N. Costce Graber found a 

 membrane separating the retina 

 from what I call the lens, and in 

 the latter nucleus-like bodies, so 

 that the lens seems to be a mass 

 of epidermal cells. 



These discrepancies I think due 

 to difference in technique. Appear- 

 ances such as those described for 

 N. CostcB I have sometimes seen, 

 and referred to imperfect preserva- 

 tion and artificial changes. Grant- 

 ing this to be the case, there is 

 otherwise great similarity between 

 the eye of that species and the 

 forms described in the present 

 paper. 



The eyes of N. cultrifera studied 



„ ., 4. „„ 4-Ua ^rv« «■ nucleus: n.p. nerve process; 



bv Carriere present, on the con- „ ■ * ^^ ui 



"j ^"^^ '- f ' _ ^./. vellow pigment; (J./, blue pig- 



trary, fundamental differences, m ^^^^,^ ^ ^^j^. ^ gj^^^jj^ ^^ ^q^. 

 that the retina is a closed spherical /. lens. 

 sac, composed, except on the cor- 

 neal side, of alternating clear, secretory, and pigmented, sensory, 

 cells with no rods. Yet sections through the visual axis might 

 show here also a central opening or pupil, and possibly other 

 methods of preparation would demonstrate the existence of 



Diagram i . — Retinal cell, rod, and 

 part of lens of one of the Nereidse. 



