208 HENRY LAURENS AND S. R. DETWILER 
a paraboloid in the slender cones. He could distinguish the 
cone nuclei from the rod nuclei by their more spherical form 
and larger size, but describes both as occupying a single layer. 
Tafani ('83) studied the retina of the crocodile, Champsia 
lucius, and found rods to be the predominant type of visual cell. 
In the anterior part of the retina there are practically no cones, 
but as the fovea is approached they become gradually more 
numerous than the rods. He found, unlike Heinemann, only 
one kind of rod. He describes the cones as being short, with a 
barrel-shaped inner segment, but with an outer segment similar 
to that of the rods, although his figures do not bear out his 
description. The differences between the nuclei of the cones and 
of the rods, which occur in a single layer, he considers too slight 
and inconstant to be considered as of any significance. 
Chievitz ('89) described in some detail the pigmented epi- 
thelium and the tapetum. In the eye of Alligator mississip- 
piensis the tapetum extends through the entire upper half of the 
retina in the form of a bright band, reaching nearly to the ora, 
while its lower margin lies about 2 mm. above the entrance of 
the optic nerve in a 32-cm. specimen. In this bright band he 
found a fovea in the form of a very superficial, narrow furrow 
with thickened edges, and running horizontally across the entire 
tapetum about 1 mm. from its lower edge. He could not decide 
whether rods as well as cones occurred. In a vertical section 
of the eye of Crocodilus intermedius the tapetum is seen as a 
longitudinal bright stripe in the middle of the pigmented epi- 
thelium. In this region the middle part of the epithelial cells 
contain a number of fine, whitish, opaque granules of guanin, 
which when removed leave the middle portion of the cells color- 
less, while the choroidal and the vitreal portions contain melanin. 
The nucleus lies in the guanin-containing portion, directly against 
the basal pigment. At the margin of the tapetum black pigment 
is present in almost the entire cell; toward the middle, the vitreal 
pigment is gradually reduced and eventually exists only in the 
form of isolated, iregularly distributed small masses, between 
which the guanin comes to the edge of the cells. In the alligator 
the pigment in the choroidal portion of the cells is sparse and 
