NO. 2.] EYES OF POLYCH^TOUS ANNELIDS. 203 



clear golden pigment spherules occupying almost exactly one of 

 the polygonal areas representing the epidermal cells as seen 

 from the surface. The pigment granules are scattered so as to 

 leave part of this area free. 



The other posterior eye had in this case ahout twice as many 



^T another case a macerated posterior eye Presents a lens 

 about one-half the diameter of a cell nucleus and .mbedded m 

 a mass of pigment granules in the end of what seems to be a 

 rX cell but which may be several cells. A s.mdar stage is 

 represented in the section (Fig. 62) where the mmute posterior 

 eye is composed of a few epidermal cells havmg clear ends next 

 the cuticle; and containing only a few pigment granules between 

 the nuclei and the cuticle. 



From the position and structure of these larval eyes and 

 from the facts observed in Nereis, we may mfer that they 

 become the adult organs. u •., 



The formation of eyes in Procaerea would then be much as m 



^ The formation of the eyes of the sexual adults, when compared 

 with the above formation of the adult eyes in the no"-=«ua 

 form arising from the egg, presents on the whole a fundamenta 

 dentity This has been studied by sectioning the new heads 

 borne upon the. sexual part of the trunk. The new head .s 

 found just posterior to the thirteenth somite posterior to 

 h™ the somites may be as many as eighty before the new 

 animal separates. Then the original thirteen somites soon 

 0™ new'ones. The eyes arise as parts of '"« d°rsa^ hicken^ 

 ino- of epidermis, making the new head (Fig. 64). As in the 

 larva, the anterior eyes appear first, and thus become larger 

 than the posterior ones and farther apart. 



In the earliest stages only the anterior eyes are present as 

 scarcely discernible pigment specks. In section each is a thick- 

 nTng of the epidermis near the base of the lateral antenna 

 (Fig 65). There is no change in the cuticle, but many elon- 

 Ltfd epidermal cells here have clear outer ends. These are 

 cut off Lm the rest of the cells by a delicate "embrane-like 

 toe passing out to the cuticle on either side. Under the h^h- 

 est powers used this is not a continuous line but mterrupted as 

 in the similarly situated structure seen in adult Eunice (Fig. 43)- 



