592 HOWARD. [Vou. XIX. 
degree than the outer segment. In a brief time granulation 
sets in, followed, as soon as the ensheathing substance of the 
outer segment is broken, by complete dissolution. The degree 
of instability of the ellipsoid is next to that of the outer 
segments of the cone. 
The paraboloid in the fresh rod of Necturus has, as its 
name appropriately signifies, a paraboloid form. As a rule 
its diameter is less than that of the ellipsoid, while the total 
diameter of the inner limb remains the same. From this 
fact it is seen that the ensheathing substance is thicker than 
that about the ellipsoid. This contractile sheath corresponds 
to the myoid, and the latter term is preferable to the word 
sheath, since the paraboloid is a separate body possibly 
possessing an independent sheath of its own. Contraction of 
the myoid undoubtedly flattens the paraboloid. <A flattened 
condition is shown in Figures 10 and 11 (Pl. 2). The para- 
boloid has a lower degree of refraction than the ellipsoid, 
but greater than the ensheathing myoid. The paraboloid 
may be isolated, and when thus separated from its normal 
surrounding structures and suspeiided in the eye fluid, it 
assumes a spherical form. Here there is no granulation 
and clouding, such as we get so quickly in most protoplasmic 
substance after death. The appearance suggests the oil 
globules of the retinal elements in some amphibians and 
sauropsidans, but this resemblance is evidently only 
superficial. 
The nucleus in the rod is often in contact at is distal end 
with the paraboloid. Its distal surface under these circum- 
stances is concave, thus conforming to the convex surface of 
the paraboloid. Except for this occasional slight depression, 
the nucleus has an approximately ovoid form. A cytoplasmic 
sheath can be quite readily detected about the distal portion 
of the nucleus. I have not been able to distinguish it at the 
proximal end in fresh rods and cones. Granulation very 
rapidly sets in here, as is the case with most nuclei (PI. 2,. 
Figs. 10, 14) mise 
