294 ANDREWS. [Vol. V. 



changes as some reagents do in Potamilla,' we could suggest 

 an interpretation of these figures that would show the eye of 

 Branchiomma to be closely similar to that of Sabella, etc. The 

 outer nucleus (9, N. 30, Fig. n, n.) and surrounding clear space 

 would thus represent an artificial product ; the second nucleus 

 (Fig. 13, n.) could readily be one of the pigment cell nuclei 

 projected out of its proper plane, while the peculiar circular 

 space left in Fig. 11, central to the striated body, would exactly 

 correspond to tne only nucleus found in the refracting cell of 

 Potamilla and Sabella. 



If some such suggestions should prove to be true, we would 

 have essential agreement in all the compound branchial eyes of 

 Annelids ; all are then monostichous. 



These compound eyes are not confined to the branchia, but 

 may occur upon the anterior part of the body, where, as in some 

 species of Placostegus, there may be pigmented areas, right and 

 left, upon six or seven somites. These areas in this case pre- 

 sent the same structure as the branchial eyes, as shown evi- 

 dently enough by the figure of Hansen (20). 



The central eyes occurring in one of the Euniciclae may, as 

 has been conjectured above, prove to be compound eyes of this 

 same type. 



These compound Annelid eyes are areas of pigmented epithe- 

 lium, and frequently correspond somewhat in position to areas 

 of pigment upon the branchial filaments. The ordinary pig- 

 ment cells of the branchiae have the pigment granules more 

 densely aggregated in their superficial parts, so that in surface 

 view such pigmented epithelium frequently presents a mosaic 

 of pigment granules outlining the adjacent cells. Clearer, 

 vacuole-like parts of the protoplasm may be present in the axial 

 or interior parts of these cells. In Sabella microphtlialma spe- 

 cial regions of such pigment cells, forming so-called "eye spots," 

 have some larger, club-shaped pigment cells, with noticeable, 

 swollen, included parts of the protoplasm, suggesting the inclu- 

 sions of Potamilla, etc., though not at all refracting and resistant. 

 These eye-like, pigment spots thus offer a possible transition 

 from common pigmented epithelium to the special, true com- 

 pound eye. 



The increase in the clear part of the cell, and limitation of 

 the pigment to the periphery, seems to have reached a maxi- 



