564 HOWARD. [VoL. XIX. 
salamander .6, dove .62, guinea pig .88, man .45—.0 (Greef 
:00). The thickness is constant for a given species and shows 
little variation even in the whole vertebrate series. Between 
the plates is a cementing substance, which becomes greenish 
instead of black in osmic acid. This cement is affected rapidly 
by certain reagents, and owing to its swelling it causes a char- 
acteristic disintegration of the outer segment into discs. This 
disintegration occurs earlier at the distal end of the segment 
than at the proximal, the difference being due to a protecting 
sheath over the latter. 
The presence of an axial fibre in the outer limb, as main- 
tained by Ritter (’59) and later called “Ritter’s fibre,” was 
questioned. Manz (’61; ’66) and Hensen (’67), however, 
sided with Ritter; but Max Schultze concluded from Zenker’s 
study of the refractive indices of these parts, that the appear- 
ance was due to a difference in refrangibility between the 
sheath and the substance of the rod. It was probably this 
opinion of Schultze which was responsible for the general 
discredit which “Ritter’s fibre” eventually met with. 
Inner Segment.—The inner segments of the rods in amphi- 
bians are usually short but as wide as the outer ones. In 
perfectly fresh condition the substance of the inner segment is 
homogeneous. Very soon after a preparation is made, how- 
ever, a cloudiness appears, which seems to be due to coagulation 
granules. In the toad and frog there is observable near the 
edge of the outer segment a characteristic body in the form 
of a plano-parabolic lens. This body, which in fishes, other 
amphibians, and birds is much broader, was given the name 
“lens-shaped body” by M. Shultze, and later was called “ellip- 
soid” by Krause, and “outer-lens” by H. Virchow. The ellip- 
soid turns brown with osmic acid. It is more strongly differ- 
entiated by further treatment with fuchsin. With this stain 
the outer limb, as well as the ellipsoid, becomes a dark red 
while the remainder of the inner limb is light red. A more 
complicated condition is found in some forms (Triton, Sala- 
mandra), in which there are present two lens-like bodies having 
