No. 2.] COMPOUND EYES OF ANNELIDS. 283 



The general position of the eyes and this division into central 

 pigmented and peripheral, clear zones is well seen in transverse 

 sections of the branchia (Fig. 20). 



Whether this position of the pigment is normal or constant 

 in life, or perhaps varying with the illumination, or withdrawn in 

 process of preparation, remains an open question. In macera- 

 tion the pear-shaped inclusions are each seen inside a clear cell 

 with the pigment as if shrunk towards the conical tip of the 

 inclusion, which it partly surrounds. 



The structure is the same here as in the last Annelid examined 

 (Fig. 21), and here also the isolated inclusions may still adhere 

 to the cuticle (Fig. 22), yet not as firmly as in 5. melanostigma, 

 for the evident reason that the point of union is much reduced, 

 often eccentric, and usually broken in preparation. 



Though the axial part of the refracting cells shows no trans- 

 verse striation, I judge this is due to the poor preservation of 

 the material as compared with that used in the above cases, and 

 that probably the structure is here also much as indicated in 

 the diagram (Fig. 2). 



A beautiful yellow Sabella taken with the preceding two has 

 branchial organs, presenting a most unexpected structure, at 

 first sight entirely different from the branchial eyes previously 

 described. 



This Annelid may be put into the genus Hypsicomus of Grube 

 (19), but does not agree with any described species known to me. 



The eye spots form a row of about thirty-four to forty red- 

 brown, elongated, quadrangular areas on each lateral face of a 

 branchial stem, extending, however, from the base to about the 

 middle of the length only, and there gradually ending as smaller, 

 less crowded specks. Each spot is about 37^. by 15 /j,., and 

 separated from the adjacent members of the row by a somewhat 

 constant interval, varying from 30 fi. to 60 yu,. ; being thus at 

 places nearly as numerous as the pairs of branchial filaments 

 there. Irregularity in the degree of separation is accompanied 

 by irregularity in direction of the long axes of these areas, most 

 being elongated in the axis of the branchia, others set diagonally 

 and even at right angles to that axis, but not with the regularity 

 mentioned by Ehlers in H. circumspiciens. Closer observation 

 of an eye shows that it is an elongated mass of pigment buried 

 beneath the surface, not projecting as in the previous animals, 



