No. 3.] VISUAL CELES IN VERTEBRATES. 581 
Pl. 3, Fig. 20). These lines have a parallel trend and ten to 
fourteen of them may be counted on one side of a rod. In 
cross sections of the outer segments (Pl. 2, Fig. 9) well defined 
circular dots are present in the periphery of the section. These 
correspond in number with the striations seen in lateral views, 
which, with other evidence, determines their character as 
definite fibers. 
In most cross sections of the outer segment there are, just 
within the circumference, vesicles of somewhat regular 
arrangement but varying in size (Pl. 2, Fig. 9, vac). After 
fixation by mercuric chloride there is no differentiation of a 
definite sheath such as is seen in osmic acid preparations. 
Now and then outer segments occur showing dark transverse 
lines at regular intervals, as well as dark plates separated 
by light lines. Fig. 24 (Pl. 3) is a drawing of such a rod. 
This was a detached outer segment and possibly had progressed 
more rapidly than the attached rods in the changes which 
bring about the plate-like cleavage of the outer segments. 
The intermediate plate appears in this material as a very 
narrow light zone between the outer segment and the ellip- 
soid. It does not take the stain and seems more refractive 
than other portions (Pl. 1, Fig. 1, dsc. im.). The fibers, 
already described, pass over it to the ellipsoid. 
The ellipsoid contains considerable stainable substance, 
being strongly stained by eosin, fuchsin, hematoxylin, ete. 
Where hematoxylin is used, the mass of the ellipsoid may be 
a homogeneous black, or this may be resolved into globules 
(Pl. 1, Fig. 1, ell. bac.; Pl. 3, Fig. 20). When the ellipsoid 
has been decolorized sufficiently to become translucent, super- 
ficial striations can be made out (Pl. 1, Figs. 1 and 6; Pl. 2, 
Fig. 7). In cross sections (Pl. 1, Fig. 6) these can be identi- 
fied as fibrils, which have retained the stain and are undoubt- 
edly continuations of those described for the outer segments. 
The ellipsoid body appears in some cases to be enclosed on all 
sides (Pl. 3, Fig. 20; Pl. 4, Fig. 33) by the light staining 
sheath substance. In most cases, however, a separation can 
