286 ANDREWS. [Vol. V. 



across. These nerves lie in, or at the boundary of, "the epider- 

 mis, in a groove, and send numerous large and small branches 

 towards the filamented side of the branchia. 



III. Historical. 



Before discussing the preceding facts concerning the so- 

 called compound eyes of certain sedentary Annelids it seems 

 advisable to review the literature upon this subject, at least as 

 far as the published figures and the less superficial descriptions 

 of the eyes are concerned. 



The existence of pigment spots, or pigmented organs, upon 

 the branchiae of certain tubicolous Annelids was too patent a 

 fact to be long overlooked, and figures of them recur frequently 

 in systematic works. 



They are plainly shown by Dalyell (l) as red spots, occurring 

 in seven or eight regular, transverse rows upon the branchial 

 apparatus of an Annelid he speaks of as Amphitrite venti- 

 labrum, and in more numerous pairs in A. bombyx. No careful 

 examination of them, however, seems to have been made till 

 Kolliker (2) studied them both in an Annelid obtained at 

 Naples, and in the one previously known to Dalyell, in Scot- 

 land ; nor was any subsequent investigation of their minute 

 structure attempted for several decades. He found in the 

 former species one " compound eye " upon each of the eight 

 branchiae, near its base. The eye is composed of fifty to sixty 

 elementary eyes, each with a cuticle, special refracting, pear- 

 shaped body, and a crystalline cone surrounded by brown-red 

 pigment. The other form, studied some years later, he calls 

 Branchiomma Dalyelli, and in this finds eighteen to twenty 

 pairs of hemispherical, projecting, compound eyes, arranged at 

 regular intervals on the outer side of each branchia. 



In each eye there are fifteen to eighteen clear, glass-like, 

 pear-shaped, crystalline cones, imbedded in granular, brown 

 pigment. 



The blunt base of each cone projects somewhat from the 

 main mass of pigment, yet some of the latter extends up to the 

 cuticle. 



The cuticle presents a depression at the centre of each lens, 

 or area, over a cone, and into this fits a small projection of the 



