554 LESLIE B. AREY 
Be | 
prs.dst.bac,-------} : 
\ _-prs.dst.con, ell.bac:-------~ 4 
== CLL COM 
MYCE D aa ae 
nae. -my.con. 
prs.dst.con:--------H--- 
eee prs.dst.bac. 
CLE CON 
Sica 
_-ell.bac. NU COMas=- sete } 
__--my.bac. 
mb.lim.ex.. 
Katharine Hill 
Fig. 3. From the dark-adapted retina of the common horned pout, Ameiurus 
nebulosus, showing the positions assumed by the rod and cone cells (X 930). 
Fig. 4 From the light-adapted retina of Ameiurus, showing the positions 
assumed hy the visual cells (x 930). The change in the length of the cone avoid 
is not as striking in Ameiurus as it is in most fishes—in the shiner, Abramis 
crysoleucas, for example, the cone myoid shortens in light to 10 per cent of its 
length in darkness. The change in the rod myoid, on the contrary, is especially 
well marked in Ameiurus, the maximum ratio of its length in darkness and in 
light being 1:10. 
ABBREVIATIONS 
ell.bac., rod ellipsoid prs.dst.bac., outer member of rod 
ell.con., cone ellipsoid prs.dst.con., outer member of cone 
mb.lim.ex., external limiting membrane _ scl., sclera 
my.bac., rod myoid st.nl.ex., outer nuclear layer 
my.con., cone myoid 
