316 University of California Publications in Zoology [Vol. il 



ment cells might readily be taken for modified sensory epithelium, 

 since a few of these peripheral epithelial cells {ep. c, pi. 14, fig. 4) 

 contain a small amount of pigment. Alternating with these are 

 elongated spindle-shaped sense cells {sens, c.) corresponding to 

 the retinal cells below the lens, with both ends drawn out to a 

 fine thread. They are longer than the epithelial cells and extend 

 one-fourth to one-third of the distance to the base of the eye. 

 These are the " Sinne.szelle " of Linko (1900). In the remaining 

 parts of the ocellus is found a variety of all these structures. 

 The basal membrane {ias.m.) becomes thickened in places and 

 gives off branches {sup. conn, tis.) into the eye. These in turn 

 give off smaller branches which lie in between the cells. These 

 thin processes probably give greater strength to the eye. Lodged 

 between them are three kinds of spindle cells: one similar to 

 the sense cells with an oblong instead of ovoid nucleus ; a second 

 very similar, with its pointed ends drawn out to a fine thread, 

 both possibly sensory ; a third with a short, thick cell-body, short 

 pointed ends, and a very large, conspicuous nucleus. Cells 

 {n. c.) similar to the last are also found lying parallel to the 

 basal membrane, or at an angle with it. These are not always 

 symmetrical in form and appear to be nerve cells, or small 

 ganglion cells. Also parallel to the base are smaller spindle cells 

 with small nuclei and ends drawn to a finer point. These are 

 the bipolar ganglion cells {hip.n.c). Interposed between the 

 main mass of cells is an entirely different form, the multipolar 

 or ganglion tj-pe of nerve cells {gang. c). It is triangular in 

 outline, with a large centrally located nucleus. At each corner 

 is a long, fine process or fibre, two of which run for some distance 

 between the other cells, and the third extends towards the basal 

 membrane. A similar one with only two processes is shown at 

 the opposite side of the section. 



The lens {Is.) fills completely the cup formed by the wall of 

 pigment cells. When isolated it forms a biconvex lens which the 

 Hertwigs (1878) believe effects a dispersal of light rays. They 

 believe it to be only a thickening of the cuticle which everywhere 

 else forms a thin transparent layer over the external surface. In 

 some forms, as Hippocrene and Sarsia, pigment granules have 

 been found in the lens, which led Agassiz (1849) to consider it 



