No. 2.] EYES OF POLYCH^TOUS ANNELIDS. 187 



and some green specimens have red pigment also. The eyes 

 studied are thus chiefly those of the mature male, either variety 

 being used ; both are about equally abundant and have the same 

 eyes. 



As in the sexual form of Nereis alacris (Fig. i), the posterior 

 eyes (Fig. 39) look upward, the larger anterior eyes downward. 

 The large anterior eyes have become so far removed ventrally 

 as to be vertically beneath the small posterior or dorsal ones. 

 The eyes are red-brown, the isolated pigment granules yel- 

 lowish. 



The lens is very conspicuous as a somewhat conical, clear 

 body, evidently connected with the cuticle by a slender stalk or 

 pedicle. This connection is also seen in sections, but as it is 

 very minute it is not often cut, and a condition like that shown 

 in Fig. 44 is more common. 



This is, however, owing to the shrinkage, not the natural rela- 

 tion. In fact, there is less protuberance of the cuticle over 

 the lens, and a distinct intervening space between the lens and 

 epidermis, save at the point where the small stalk is. The true 

 condition is then more like that indicated for another annelid in 

 Fig. 41. 



When teased out fresh, the lens is a solid, homogeneous, 

 highly refracting mass, and is markedly bilobed, the larger lobe 

 filling the optic cup, the smaller projecting from the pupil. 



The connection with the cuticle is obvious even in macera- 

 tions ; when potash is added, the lens dissolves save for a granu- 

 lar matrix and a few oil-like drops, but this faint residue remains 

 attached firmly to the cuticle at one point. 



Haematoxylin stains the lens readily, osmic acid gives it a 

 brown color, while nitric acid turns it orange. In hardened 

 specimens it is brittle and refractory. 



The retina (Fig. 44) has the same structure as in the eye of 

 a young Nereis (Fig. 21). When macerated the cells seem to 

 carry much of their pigment upon the outside, where it is easily 

 removable (Fig. 40), but the use of high powers convinces one 

 that there are also many yellowish granules in the axial parts of 

 the cells. The part readily removed is to be regarded as also in 

 the cells, but in the superficial parts only. 



Most of the cells are alike as in Fig. 40 : the peculiar branch- 

 ing or anastomosing cell in the left was observed but once. 



