No. 2.] COMPOUND EYES OF ANNELIDS. 285 



spheroidal refracting body, and pigmented like the adjacent cells 

 that apply their inbent ends against the lateral sides of the 

 cuticular ingrowth : the nucleus of this cell, also, has a charac- 

 teristic triangular section. 



A series of sections at right angles to the long axis of an 

 eye leaves no doubt as to its structure. In one series there 

 were twelve sections, each 5 /x. thick ; of these, beginning at the 

 outer end of the eye, the first four or five cut only the common 

 epidermal cells and the oblique base of the refracting body 

 where still continuous with the cuticle : passing inward, this 

 body is next represented by a series of perfectly circular .disks, 

 separating more and more from the cuticular surface, diminish- 

 ing rapidly in diameter, and entirely surrounded by epidermal 

 cells applied to its circumference, and becoming more and more 

 pigmented towards the apex of this body. Thus, in the 8th 

 and 9th section we find the apex (Fig. 26) far removed from 

 the cuticle, and surrounded by three pigment cells. The next 

 two sections do not cut the refracting ingrowth, but the ter- 

 minal pigment cell and its spherical refracting body, which 

 is circular in transverse section and much larger than the 

 truncated apex of the above ingrowth. Finally, the nucleus 

 of this section is cut, forming the end of the long axis of 

 the eye. 



The conical shape of the long refracting body deduced from 

 the above section is evident in macerations (Fig. 27), where its 

 enlarged base is entirely continuous with the cuticle, and its 

 apex as abruptly truncated as in the inclusions of Potamilla and 

 Sabella, which it essentially resembles. 



A brief reference to the branchiae of the only member of the 

 Serpulidce examined, Hydroidcs dianthus, Verrill, so common at 

 Wood's Holl, will show that there are here no eyes such as 

 above described, nor, in fact, any obvious organs of sense. 



Though the branchiae are usually most brilliantly colored 

 and variously banded, yet all the pigment is readily soluble in 

 alcohol, and leaves no dark spots of any kind as indications of 

 possible sense organs. Moreover, careful examination and 

 sectioning shows only the structure indicated in Fig. 28, where 

 the thick cuticle and elongated epidermal cells present no dis- 

 covered eye-like modification ; the two peculiar structures occur- 

 ring in the angles of the section being longitudinal nerves cut 



