DAL LESLIE B. AREY 
amphibians a slight shortening of the inner member probably 
occurs, whereas in fishes (figs. 3 and 4, my. bac.), and birds there 
is a marked elongation. 
After strong illumination, Ewald und Kihne (’78) first ob- 
served a change in the outer member (ef. figs. 3 and 4, prs. dst. 
bac.) of the frog’s rod, in which a thickening or swelling was said 
to take place. Angelucci (’84) measured the lengths of the rod’s 
outer members and found that they were shorter in the light; 
later (90) he confirmed this result by measurements of the large 
rods of the salamander, where the difference in length was more 
striking. Arcoleo (’90) and Garten (’07) reported similar con- 
ditions for the toad and the frog respectively. 
The inner member of the frog’s rod likewise shortens when 
exposed to light, as was recorded by Angelucci (’84) and Grade- 
nigro (’85). Later, in 1890, Angelucci borrowed the term ‘myoid’ 
which Engelmann had given to the contractile portion of the 
cone’s inner member and applied it to the corresponding part 
of the rod (figs. 3 and 4, my. bac.). Recently Lederer (’08) has 
challenged the result of the previously named workers. Ac- 
cording to his statement the rods of the frog elongate in the 
light as do those of fishes and birds. Arcoleo (’90), on the other 
hand, using pithed toads, observed conditions similar to those 
reported by Angelucci and by Gradenigro, for he states that in 
the light the rod’s inner member became ‘broad and short.’ 
In connection with these conditions among amphibians should 
be mentioned the work of Stort (’87), who first asserted that in 
the dark the nuclei of the rods in Triton migrated partially 
through the external limiting membrane and thereby caused 
the whole rod to become extended, whereas in the light these 
nuclei lay completely within the outer nuclear layer. The 
contractility of that portion of the rod cell between the rod 
nucleus and the external molecular layer was believed to cause 
these movements. Angelucci (’90) made similar observations 
on the salamander. These conclusions relative to positional 
changes were preceded by the earlier observations of Czerny 
(67) and especially of Gradenigro (’85), who merely recorded 
changes of form in the nuclei of the external nuclear layer. 
