a shallow-water species (4–70 fathoms). C, lens; V, crystalline cone; R, rhabdom; N, nerve. (After Beddard.)
The eyes of all the deep-sea species are relatively larger than those of the shallow-water ones, except Serolis gracilis, whose eyes seem to be disappearing.
But these large eyes of the deep-sea species of Serolis are not capable of any greater perceptive power. In fact, the evidence of degeneration they show, both in minute structure and in the diminution of pigment, proves that they can be of very little use to these animals for perception.