5606 HOWARD. [VoL. XIX. 
exceedingly unstable and show the same plate-like structure 
as the rods, but owing “to a sheath the disintegration is not 
as rapid. This fibrillar sheath in the cones, as in the rods, 
is easily demonstrated to be a prolongation from the inner 
segment. This inner segment shows the same complexity as 
that of the rods, possessing a distal ellipsoid (linsenformigen 
Korper) and a proximal paraboloid (“blassere innere 
Halfte’). In the frog and also in Sauropsida generally, there 
is present between the outer segment and the ellipsoid a 
highly refractive, colored, spherical body called the oil globule 
(“pigment Kugel’). Max Schultze (722, p. 1003) found 
internal longitudinal fibres, in addition to peripheral fibrils, 
occupying the whole thickness of the inner segment of the cone 
in man. He was able to follow these from the beginning of 
the outer segment to a point short of the external membrane. 
Their further connections he was unable to make out. 
Nuclet.—While in fishes and mammals the nuclei of the rods 
differ from those of the cones, in amphibians conspicuous 
differences are not apparent. The nuclei are arranged in two 
layers in both Rana and Bufo, but in a single layer in Triton 
and Salamandra. In frogs and toads the nuclei of the rods 
are commonly close to the external limiting membrane, while 
those of the cone cells are crowded into the second layer. 
Hoffmann (’75) described a thin granular cytoplasmic sheath 
about the nuclei and says there is a proximal extension (cone- 
foot) of the sheath into the outer granular layer. This exten- 
sion possesses, according to somewhat inconstant appearances, 
a terminal spherule having a rough or ragged surface. 
Double Cones, first described by Hanover (’40), are found 
in all vertebrates except mammals. They consist of two cones 
applied along a part of their lateral surfaces. In Amphibia 
as well as in Sauropsida there is a conspicuous difference 
between the cones of a pair. One of these is longer and egg- 
shaped, it is called by German authors the ‘“Haupt-zapfen:” 
the other is shorter and retort-shaped, it is known as the “Neb- 
en-zapfen.” In triton the Haupt-zapfen possess ellipsoids only, 
