570 HOWARD. [Vou. XIX. 
to the distal end of the outer segment, which is turned towards 
the pigment cells. In the red rods, the fibres are described 
as peripheral, starting from the rod foot and extending over 
the nucleus in the thin mantel sheath. Between the nucleus 
and external limiting membrane, they form a loose fibril group, 
but on reaching the membrane they become entirely peripheral, 
lying in the sheath of the inner and outer segments for the 
rest of their course. A granular cone proximal to the ellipsoid 
may be a new feature for the inner limb, but is probably 
identifiable with the paraboloid. The outer segment is stated 
to contain internally a homogeneous elastic mass, breaking 
easily into cross plates, but again, an appearance of cross 
striping is explained as due to a regular interruption of a 
“color mantel” on the peripheral neurofibrils. The club-shaped 
rods differ from the red rod in that the neurofibrils traverse 
the whole substance of their outer segments. As to the cone 
cells, Schneider says of the neurofibrils in their outer segments : 
“Diese Neurofibrillen durften sich im Aussenglied in Windun- 
gen legen.” Otherwise the condition of the fibrille is the 
same as in the rods. 
Greef (:00), who depended chiefly upon osmic acid as a 
fixing agent, finds no fibrils. He describes, however, some 
details of interest in the structure of the rod, e. g., the 
“Zwischenscheibe,”’ a plate between the outer and inner seg- 
ment; also the occasional appearance of two “Zwischen- 
scheiben” between plates of the outer segment, and a sheath 
over the inner and outer segments. Levi (:00) holds much 
the same views as Greef as to the structure of the visual cells. 
Hesse (:03), in a paper read before the Deutsche Zoolog- 
ische Gesellschaft, reports the presence of spiral neurofibrils, 
and in a later paper he (:04) gives his results on teleosts, 
selachians, amphibians, and reptiles more fully. Hesse 
declares for two systems of fibrils, both of which he finds 
present in rod and cone cells. The first, which appear in 
general as parallel longitudinal lines, he believes to be thicken- 
ings of the sheath, confined to the periphery, where they have 
