366 J. 8. BODEN AND F. ©. SPRAWSON. 
epithelium which in the region of the tapetum lucidum con- 
tains no pigment, the specimens were first stained with dilute 
magenta before being mounted. 
The specimens were taken from the eyes of the sheep, ox, 
rabbit, kitten, pig, frog, and hen. In all cases the results 
were the same. Hexagonal cells are certainly the most 
numerous ; heptagonal cells come next, and scattered at inter- 
vals throughout-a preparation, cells with four, five, eight, nine, 
ten, and eleven sides are also found. In all cases there is 
never anything of the nature of a gap; the mosaic appears to 
be always perfect. This is true for all parts of the epithelium 
—that is to say, in the cells richly laden with pigment in the 
tapetum nigrum, and also in the unpigmented cells over the 
tapetum lucidum when that is present. | 
We included the hen in the list of animals the eyes of which 
we examined, as it was from the retinal epithelium of this 
animal that Max Schultze’s figures were drawn. Here the 
shape of the cells is. certainly much more uniform than in 
mammalian eyes, but we saw amidst the hexagonal cells several 
with five, seven, eight, and nine sides. 
There can be no doubt that the polygonal shape of the cells 
is due to mutual pressure, and if all the cells were of the same 
size they would be necessarily hexagonal. In the process of 
growth, however, some cells, receiving presumably more nutri- 
ment, grow to a greater size than their fellows. The result of 
this is that the bigger cells come into relation with a larger 
number of ordinary sized cells, and so become more than six- 
sided ; and in a similar manner the smaller cells are less than 
six-sided. This view is fully borne out by a number of 
measurements we have made. The number of sides in a cell 
varies directly as its size. 
We give below the measurements we have made in the case 
of the sheep and ox. The measurements were made with the 
aid of a camera lucida, and the numbers below give the longest 
and shortest diameter of the cells. 
