292 ANDREWS. [Vol. V. 



Certain unusual ventral eyes of the " Palolo worm " may, I 

 think, be also regarded as having much of the structure found 

 in various branchial eyes, at least so I would interpret the 

 figures given by Ehlers (8). 



These organs are figured as dorsal pigmented spots by 

 Macdonald (13) and regarded as dorsal glands by Ehlers ; yet 

 Spengel (12, p. 43) states they are undoubtedly eyes, and situ- 

 ated as a median series, one for each somite, upon the ventral 

 nerve ganglia. 



Such an important extension of these compound eyes from 

 the lowest tubicolus Annelids to the Eunicidas is, however, 

 scarcely to be ventured upon without further knowledge of 

 the structure in question. 



IV. Conclusions. 



The eyes of Potamilla are numerous areas of modified epi- 

 thelium of the main stems of the cephalic branchiae. Each is 

 composed of elongated, pigmented cells, a few of which are 

 characterized by the possession of peculiar refracting bodies 

 in their outer ends and modified axial parts. These latter cells 

 are presumably the sensory cells, and have pigment only in 

 the superficial part of the protoplasm, as shown in the diagram 

 (Fig. 1). The eye is compound, since each such sensory element 

 is separated from its neighbors by intervening pigment cells. 



In a species of Sabella and of Dasychone the eyes have 

 essentially this same structure. As represented in diagram 

 (Fig. 2) the pigment is found deeper in the substance of the 

 cell, and the refracting body is actually continuous with the 

 cuticle. 



In a species of Hypsicomus the branchial eyes are not 

 compound, but comparable to one of the elements of the 

 above eyes. 



The single refracting, cuticular ingrowth resembles one of 

 the numerous inclusions of Sabella, but is not contained within 

 its cell. This cell may be regarded as sunk beneath the sur- 

 face, and shortened in proportion to the elongation of the re- 

 fracting cone. Thus the axial part of such diagrams as 1 and 2 

 would be shortened also, and be represented in Hypsicomus by 

 the single spherical body found in the cell between its nucleus 



