584 HOWARD. [VoL. XIX. 
the irregular separation of plates by vacuoles. Three of the 
latter are shown in Figure 21 (PI. 3) two on the left and 
one on the right. Sometimes the spiral appearance is much 
more striking, as if there were two fibers closely parallel, 
and suggests some of Hesse’s ( :04) figures. A common 
appearance presented by the outer segment of the cone is 
shown in Figure 20 (Pl. 3); here the tip only is dark and the 
proximal portion is marked by irregular lines, probably cleav- 
age effects. 
I have observed with certainty no intermediate plate in the 
cones of Necturus. 
The ellipsoid of the cone differs from that of the rod in 
form, being of greater length and smaller diameter. The 
stain is retained longer and the resolution of the staining mass 
into globules is more apparent than in the rods (Pl. 1, Figs. 
1, O50E1 3), Fie, 21 -eP ls, Fis. 30 seran. ella): 
The paraboloid is smaller than in the rod and more con- 
stantly ellipsoid or ovoid. ‘The sheath is relatively thicker and 
fibrils are more easily seen than in the rods. In cross sections 
the fibrils appear in two layers, an inner and an outer (PI. 1, 
Fig. 44). No evidence of “difference in these ‘circles on 
fibrils could be detected with certainty. 
The myoid, or contractile portion, between the nucleus and 
paraboloid is more distinct here than in the rods. The course 
of the fibrils over the nucleus corresponds to that in the rods. 
The nuclei themselves are commonly more pointed at the distal 
end than those of the rod are. 
Double Cones.—As in other amphibians and in the other 
vertebrate groups except the mammals, there are in Necturus 
the remarkable elements called double cones. In fishes, so 
far as I have observed, the two cones of any pair are nearly 
alike, but in Rana and in Necturus they are in some respects 
quite different. The longer one (PI. 1, Fig. 2, 4) for con- 
venience may be called the far cone (con. dst.) and the other 
(Fig. 2, B), which for the most part lies nearer the mem- 
brana limitans externa, the near cone (con. prx.). These are 
