214 ANDREWS. [Vol. VII. 



may have been in part due to the presence of a hard skeleton 

 immediately beneath the epidermis. 



Though this is the character of the branchial eye in general, 

 the peculiar eyes met with in Hypsicomus present what may be 

 regarded as a transition towards the "camera" eyes of the 

 annelids. Each eye here has a single conical lens or rod and 

 lens combined, continuous with the cuticle and springing from a 

 single cell at its apex. The pigmented cells round about this 

 elongated lens are, however, applied against it as if taking part 

 in its formation. The eye might thus be compared with 2, Dia- 

 gram 2, supposing only one cell to have a rod-lens and the adja- 

 cent cells bent over towards this refracting part. This eye is 

 then formed upon the sunken-in type, and seems to have arisen 

 without invagination. At the same time the central cell of this 

 peculiar eye presents a refracting inclusion comparable to that 

 found in the separate cells of the compound eye. 



There is thus agreement in all the eyes of Polychaetae to the 

 extent that the visual cells are pigmented, epidermal cells having 

 some sort of clear, refracting material next the cuticle. 



In the compound eye this is within separate cells. In Hypsi- 

 comus it is in one cell and also forms a single cuticular ingrowth. 

 In the camera eyes of the higher Polychaetae it forms rods and 

 lens structures, together with various ingrowths of the cuticle. 



Not knowing how far the annelid cuticle is a true secretion 

 from the cells, rather than a transformation of their ends, no 

 sharp distinction has been drawn between it and the various 

 refracting bodies so often continuous with it. 



Johns Hopkins University, 

 May 23, 1 891. 



