RETINA OF ALLIGATOR MISSISSIPPIENSIS 
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found in the turtle retina. The inner segment consists of a 
short broad myoid, a broader refractive paraboloid, and an 
elHpsoid, while the outer segment is relatively short and conical 
(fig. 5). This type of cone is found particularly in the posterior 
and ventral portion of the retina. The second type of single 
cone (not very numerous), which is found only in the ventral 
portion of the retina, has a considerably longer myoid and a 
Fig. 5 A portion of the visual layer showing rods and large single cones. 
X 935. Drawing made at about 2.5 mm. above the entrance of the optic nerve 
(level C, fig. 1). 
Fig. 6 Elongated single cone and a neighboring rod taken from the ventral 
portion of the retina. X 935. Animal in darkness for twenty-four hours. 
Fig. 7 A double cone taken from the lower portion of the retina. Animal 
in darkness for twenty-four hours. X 935. 
Fig. 8 A double cone taken from the tapetal portion of the retina. Animal 
in diffuse light for seven hours. X 935. 
narrower paraboloid. The conical outer segment is long, slender, 
and pointed (fig. 6) . 
The double cones consist of a larger and a smaller member. 
The former are very similar in shape to the large single cones. 
The latter is characterized by a long slender myoid and the 
absence of a paraboloid and has not been observed to occur 
singly (figs. 7 and 8). All cones lack oil drops, differing in this 
respect from those of the turtle and lizard. 
