2IO ANDREWS. [Vol. VII. 



Unfortunately, the youngest stages observed (Fig. 29) have 

 already much of the character of the adult eyes. The distinc- 

 tion of rods and lens is, however, less marked, while the whole 

 organ is very minute. 



An early connection of lens and cuticle is indicated by the 

 fact that these small eyes have already acquired stalks as long 

 and thick as those of the adult, though the retinal cup is very 

 much smaller. 



In the example figured there are, abnormally, two posterior 

 eyes on this one side of the head, each eye having its separate 

 stalk extending from the lens to the cuticle. 



IV. SUMMARY AND CONCLUSIONS. 



An examination of the eyes in a majority of those fami- 

 lies of the Polychaetae in which they are well developed, has 

 shown that there is fundamental agreement in the following 

 general characters. 



The eyes are epidermal organs and generally remain con- 

 nected with the epidermis. 



Each is a pigmented cup filled by a refracting mass which 

 projects more or less from the orifice, the pupil, and there usu- 

 ally comes into contact with the cuticle. 



The pigmented cup is composed of a single layer of epidermal 

 cells, forming the retina, all essentially alike, though some may 

 be much attenuated. 



These cells have nerve processes and contain a pigment that 

 is yellow, red, blue, or black, and may, perhaps, be converted 

 from a lighter into a darker color, two appearing in some cells. 



Each cell bears a clear rod, having an axis continued from 

 the cell through the densest part of the pigment ; these rods 

 form the peripheral part of the refracting mass, but are part of 

 the retina. 



The remaining, central, refracting material is more liquid in 

 nature ; it may be nearly a homogeneous lens, or divided into a 

 denser lens proper near the pupil, and a less dense part, vitri- 

 ous body, next the retinal rods. 



The refracting mass is often continuous with the cuticle and 

 by the intervening rods with the retina also. 



It may appear as a liquid secreted by the retinal cells or may 



