No. 2.] COMPOUND EYES OF ANNELIDS. 28 1 



of uncini which would refer it to the genus Sabella, as restricted 

 by Malmgren (15). As Ehlers has noted, there are here four 

 or five pairs of conspicuous dark red eyes upon the outer side of 

 each branchial stem, the pairs separated by a very long interval, 

 and the two eyes in a pair not usually exactly opposite, but one 

 more distal, the other more proximal. Each organ has about the 

 same size as that of Potamilla, and has a similar position at the 

 union of the lateral and outer faces of the branchia, but more 

 upon the outer face (Fig. 17). Moreover, each is less prominent, 

 more elongated longitudinally, though in this section across its 

 distal end it appears more prominent. Here, again, these organs 

 occur upon parts of the stem bearing the pigmented filaments ; 

 that is, in the general regions of the transverse color bands. 



As the material was not especially prepared for this work, 

 these eyes could not be as satisfactorily examined as in the 

 above cases, but surface views and sections, pigmented and 

 depigmented, give the following results. 



The eye has the same structure as that of Potamilla, with 

 but few minor differences. 



The cuticle is very thick, compared to the above case, and 

 sometimes presents slight pits, as seen in surface view or on 

 section, which are due to the fact that the refracting inclusions 

 are not only firmly attached to but even continuous with the 

 cuticle, so that a depression may occur at the centre of the base 

 of each inclusion. Presumably, this is due to shrinkage in 

 preparation, but may possibly exist in the living eye. The 

 attachment does not extend over the entire base of the conical 

 inclusion, but leaves a peripheral protoplasmic area, as in Pota- 

 milla, though but a very thin one indeed (Fig. 18) between part 

 of the base and the cuticle. 



Macerations of this hardened material leave no doubt as to 

 this continuity of inclusion and cuticle (Fig. 19), the conical 

 mass being frequently obtained firmly attached to the cuticle, or 

 torn off and showing a distinct scar. 



As far as could be made out without the aid of fresh material 

 for maceration, the refracting cells have otherwise the same 

 structure as in Potamilla, the axial portion, however, presenting 

 more numerous and fainter transverse areas of clearer and less 

 refracting material. Hence the idea of this cell would be dia- 

 grammatically expressed somewhat as in the accompanying 



