1 84 ANDREWS. [Vol. VII. 



in the small amount of matrix or fused cell wall between the 

 rods. 



Such sections across the central zone of nuclei show them 

 to be much smaller than the peripheral nuclei of the common 

 larger retinal cells ; these smaller nuclei seem generally to be 

 those of the attenuated cells (Fig. 43). 



Arabella op alma Verrill. 



The eyes, as seen through the thick cuticle and epidermis, 

 form a transverse series of dark spots, usually four, sometimes 

 six. The pair nearest the mid-line is much the largest, at least 

 twice the diameter of the outer. When six are found, the outer- 

 most are much the smallest. The pigment is very dense and 

 dark red or red-brown. 



All these eyes lie imbedded in the dorsal, ganglionic part of 

 the brain separated from the surface by cuticle, epidermis, and 

 brain substance, and, in most places, by an intervening part of 

 the body cavity (Fig. 47). 



The structure is as in Marphysa, save that the lens is scarcely 

 at all developed, and no connection with the cuticle is discover- 

 able. The optic cup is partly filled by an intrusion of cells 

 somewhat resembling those forming the inner cornea or pupil 

 in Marphysa (Fig. 35), but, in part at least, like the ganglion 

 cells of the surrounding brain. 



The retina presents long and short, thick 'and slender cells, 

 as in Marphysa ; the soft rods are intermingled with slender 

 fibres resembling those of Marphysa. 



The two largest eyes are often very irregular ; the intrusion 

 of brain cells may penetrate through the retina in such a way as 

 to cut off a few pigmented retinal cells from the rest. 



These insulated retinal cells surrounded by brain cells have 

 no rods, but are merely elongated, pigmented, columnar cells. 



There is thus some reason to believe these eyes to be degen- 

 erating. ^ 



1 An examination of Diopatra cuprea, Clpd., confirms the absence of eyes in this 

 genus. The Nackenwukte {Spengel, Oligognathus. Mith. z. s. Neapel. 3.) are, how- 

 ever, very evident as a pair of horseshoe-shaped cihated grooves, each embracing a 

 rounded elevation. The cuticle in the groove is markedly thin and perforated by the 

 cilia from a ridge of elongated, modified epidermal cells. These are connected with 

 nerves, and so arranged as to present the outlines of a " taste-bud " in transverse 

 section. 



