No. 2.] COMPOUND EYES OF ANNELIDS. 289 



figured as having one or two clear bodies imbedded in pigment. 

 In all the figures the refracting bodies are simply spheroidal or 

 somewhat elongated structures, projecting somewhat from a 

 pyramidal mass of pigment. 



Such compound eyes, or simple eye specks of unknown struc- 

 ture, occur upon the branchiae of many Annelids, but not always 

 upon closely related forms, judging from the figures and accounts 

 of systematists. Thus Grube (6) finds protuberant eyes in a row 

 upon the branchia of Sabella (Potamilla) polyopJitJialmns, a spe- 

 cies closely related to P. reniformis, Malmg. ; yet they are said 

 to be absent in P. neglecta, Malmg., and P. Torelli, Malmg. 



Again, Serpula chrysogyrus, Gr., has seven or eight eyes on 

 each branchia, the eye having twenty-seven round lenses cover- 

 ing a circular area without pigment (in preserved specimens), 

 but sending a conical streak towards the centre of the eye from 

 each lens. 



Most Sabellas with dorsal processes upon the branchia are 

 said to have eyes, but 5. decora, Sars., has none. Eyes are fig- 

 ured in Sabella (Dasychone) cingulata, Gr. ; .S. oligopJithalmns, 

 Gr., has only two eyes on a branchia ; 5. acrophthalmus, Gr., 

 has but one, at the end ; 5. serratibranchis, Gr., has only 

 black spots not regarded as eyes. Moreover, in Myxicola 

 ommatoplwra, Gr., though not occurring elsewhere in this genus, 

 there is a pair of eyes near the tip of the branchia. 



Fortunately, Semper had made notes upon this species, in 

 the Philippines, from which it appears that these compound eyes 

 may be regarded as special collections of red pigment spots 

 found separate elsewhere upon the branchiae. Each eye con- 

 tains crystalline cones with spheroidal bases and elongated, 

 conical apices, surrounded by red-brown pigment, and ending 

 as delicate threads borne by the cartilaginous skeleton. 



Although the branchiae are ciliated, the convex surface of the 

 eye is not, " ist dafur mit eigenthiimlichen langen, wie es scheint 

 starren Borsten dicht besetzt, welche wohl als besondere Tast- 

 organe aufzufassen sein werden ! " 



As the tissue changed so quickly, nothing could be made out 

 as to the connections of these hairs. 



In the systematic work of Ehlers (8), also, we meet with figures 

 and notices of the general anatomy of such compound eyes. 



Thus the eyes of Branchiomma bioculatum and Br. lobifera, 



