No. 2.] EVES OF POLYCH^TOUS ANNELIDS. 209 



Polygordius. 



Considering the simplicity of Polygordius, whether ancestral 

 or secondary, it is interesting to find its larval eyes closely 

 resembling those of Polychastae. Thus, in a section of the apical 

 plate (Fig. 68), each eye-spot is a cup of large yellow-red pigment 

 granules, partly surrounding a clear, refracting lens, that extends 

 up to the cuticle, while the surrounding nuclei suggest that the 

 eye is composed of a few ectoblastic cells. When depigmented 

 (Fig. 6^), there is a clear space representing the pigmented 

 region, while the faintly discerned cell boundaries point plainly 

 to the conclusion that the whole eye is made up of a few long cells 

 having refracting substance at the cuticular end, a large nucleus 

 in the other end, and pigment in the intermediate portion, 



Hatschek (19) figured the larval eye of Polygordius as a thin 

 pigment layer over the inner side of a spherical refracting body 

 or lens, in which nuclei are seen. He regarded the lens as 

 probably made up of clear prismatic cells with small, faint 

 nuclei, but could not decide if the pigment was in those cells, 

 or in the surrounding cells of the apical plate. 



In the figures of Fraipont (20) the pigment is a thicker layer, 

 the lens a projecting mass composed of two clear halves side by 

 side, and each containing in its outer end a body that is probably 

 the nucleus spoken of by Hatschek. 



Until these eyes are reinvestigated, and those nuclei-like struc- 

 tures shown to be actually nuclei in the cuticular ends of the 

 component elements of the lens, I am inclined to regard the 

 true nature of the eye that indicated in Fig. 6^, and to consider 

 the clear ends of the few cells composing it to be the parts seen 

 from the surface as a bilobed or as a single lens. 



In addition to the study of the formation of eyes in larvae and 

 in buds, there is a third method that has not been sufficiently 

 utilized in the annelids. A few observations were made, how- 

 ever, upon the formation of eyes in regenerated heads of the 

 species of Amphinome mentioned in the second part of this 

 paper. 



From the large number of individuals collected at Green 

 Turtle Cay, Bahamas, it was possible to pick out some in which 

 the heads had been lost, and were in process of regeneration 

 along with a varying number of anterior somites. 



