580 HOWARD. [VoL. XIX. 
That these are clefts and due to the effect of the reagents, 
is indicated by the inequality of their depth and their absence 
in the osmic-acid fixation. The outer segments of the cones 
are as a rule poorly preserved, but show a cross striation 
with a tendency to an arrangement of the bands in pairs. 
3. Corrosive-Acetic Material. 
After trying a solution of mercuric chloride with different 
proportions of acetic acid, the best results were obtained from 
a saturated aqueous solution of mercuric chloride containing 
5 per cent. of glacial acetic acid. The fluid was injected 
into the blood vessels, as already described, and the eye was 
immersed in the fluid for from 24 to 48 hours. I believe a 
short fixation with this fluid is not in general sufficient, not- 
withstanding theoretical considerations (Mann, :02). I have 
arrived at this conclusion empirically from the results of 
experiments by others, as well as by those I have made myself. 
After the sections were cut they were stained on the slide 
by either the iron-alum-hematoxylin process of Heidenhain 
or by Mallory’s (: 00) triple stain. In the-former case long 
staining of 40 hours in old hematoxylin was followed by 
decolorization so as to give on the same slide as great a 
range as possible between a strong stain and complete decolor- 
ization. Extremes are shown in Figures 1 (Pl. 1), 20, and 
2a nC ies), 
i Ne CUS: 
Rod Cells—The outer segments of the rod retain a slight 
stain, mostly in the form of reticulations apparently due to 
a very fine net-work. This is accentuated into stronger lines 
by a condensation due to the formation of vacuoles (Pl. 1, 
Fig. 1; Pl. 3, Fig. 20). In well preserved rods longitudinal 
striations are visible at upper and lower focus and usually 
more apparent in the latter (Pl.-1, Fig. 15 Pl:2; Fies. 7, a: 
