$6 Journal of Comparative Neurology. 



sedentary Polychaetes. He found these organs in Potamilla 

 to consist of an area of cells each of which has a basal process, 

 a nucleus in the basal part of the cell, and a larger peripheral 

 process containing a large refractive body. Each refractive 

 body is usually firmly attached to the cuticula. There are some- 

 times other "inclusions" between this apical refractive body 

 and the nucleus. Each cell is covered with pigment granules. 

 Andrews experimented with these eyes to see if they were phos- 

 phoresent organs with but negative results. Here then, in the 

 Polychaetes, is a case of a simple eye whose cells closely re- 

 semble those of the spiral organs of Nereis. If the simple area 

 in Potamilla became invaginated, the peripheral ends of its cells 

 spirally arranged, and the bodies of its cells farther removed 

 from the cuticula, we should have, except for the presence of 

 pigment, the spiral organ of Nereis. 



In a later paper, Andrews ('92) gives an account of the 

 true eyes of many Polychaetes. In all of the forms studied 

 macerations showed that the retinal cells were the nerve-cells, 

 that the base of each cell was prolonged into a nerve-fiber, and 

 that the peripheral end bore a slender refractive rod. In the 

 Syllidae, it could be further seen that the lens was made up of 

 the refractive peripheral ends of the retinal cells and that the 

 entire organ was attached to the cuticula by a stalk which 

 probably represented an invagination. There is also strong evi- 

 dence that the lens of the eyes of all Polychaetes is composed 

 of separate elements — elements which are but the transformed 

 peripheral ends of the retinal cells. Andrews' figure of the eye 

 of Lepidonotus is strikingly like the appearance shown in a sec- 

 tion of a poorly preserved spiral organ. Each of the retinal 

 cells of this form bears a refractive body at its tip and these 

 bodies, closely packed together, constitute the lens. 



Hesse ('99) has lately re-investigated the eyes of Poly- 

 chaetes. One of the simpler ones — the "Augenflecken" of Ran- 

 zania sagittaria in several respects closely resembles the spiral 

 organ of Nereis. It has a central solid cylinder which appears 

 to be an invagination of the outer layer of the cuticula and 

 which corresponds to the central tube of the spiral organs. 



