No. 1.] EVES OF ARTHROPODS. 123 
ment of the cells on one side of the furrow (Fig. 81). It is there 
seen that the terminal edges of the broad rods trend toward the 
centre of the newly developed lens. The latter is placed so as 
to throw light upon the vertical furrow. But this condition is 
not permanent; in the adult, the lens is horizontal, and its 
axis is directed toward the bottom of the eye. By this change, 
the amount of light that falls upon the vertical furrow is very 
much reduced. 
The nucleated ends of the corneagen cells never lie in front 
of the furrow, but always to one side of it. 
The vetinophore of eyes I. and III. are like those of eye V.: 
The secondary nucleus is always situated beyond the primary 
one, in the terminal quarter of the cell. 
It is not so easy to detect the secondary nucleus in the gigan- 
tic cells as one might suppose. Their flattened ends make 
it difficult to roll them when isolated, so that one cannot view 
the same cell from different points. Moreover, they have a ten- 
dency to stick together in great flakes that appear, owing to the 
excessive thinness of the cells, to consist of but one retinophora, 
when they may contain half a dozen or more. But in spite of 
these difficulties, I have seen enough to convince me that they 
are double cells and that the secondary nucleus is situated in 
their expanded and flattened ends about half way between the 
primary nucleus and the rod. 
Although I have not made any extended observation on the 
structure of the retinophorz in the vertical furrow, their intimate 
connection with those of the horizontal retina, as shown by the 
early stages of development, and the presence of the double 
rods, leave no room to doubt that they have the same structure 
as the other retinophore. 
In only one instance have I seen anything like ganglion-cells 
in the retina. It was a small tripolar cell, with an outward pro- 
longation extending along the sides of a retinal cell. Both cells 
were firmly united with each other, and were found among a 
great many isolated ones from all the eyes, so that it was impos- 
sible to determine to which retina it belonged. It was (Pl. X., 
Fig. 58, 2) very much like the tripolar cells found by me in the 
retina of Haliotis. : 
I have looked for these cells in sections, but have never 
found any trustworthy evidence of their presence. I regard 
