340 
preventing the bird from becoming accustomed to a fixed spot for 
its food-box (for this purpose [ employed siskins exclusively). I 
now however gave the food-box a visible mark, to distinguish it 
from the empty ones. 
1. First of all, I pasted black paper over the flap of the food 
box, the remaining ones being of bright tin. In a few minutes 
the bird had learned that the seed was behind the black flap. And 
in an astonishing short space of time a bird that has first been 
trained to look for the seed box, according to its position, seems to 
have forgotten this and it learns that the seed is behind the black 
flap. By repeatedly hanging this in front of another box, the bird 
is literally taught to fly after this black flap and exclusively or almost 
so, to tip up this flap to look for its food *). 
2. In a second series of experiments the flap of the food-box 
was pasted over with a blue paper. The flaps of the remaining 
empty boxes were also pasted over with blue paper, with blue of 
a different shade however. The result was that in a relatively sbort 
space of time the bird had learned again to go for its food to the 
box with the flap pasted over with blue of a particular shade, dis- 
tinguishing it from the remaining flaps. The difference was scarcely 
perceptible: in a series of experiments | used blue N°. 1186 of the 
well-known coloured papers of Baumann for the empty boxes, and 
N°. 1187 for the food box (food-colour)?), this difference is barely 
perceptible to the human eye. (1187 is the merest shade darker). 
3. A series of controls was still taken with green papers of dif- 
ferent shades. It appeared that the siskin distinguished as food colour 
N°. 985 from green N°. 984, from BauMmann’s scale. 
4. In a subsequent series of experiments I selected an extremely 
small token of distinction for the food box. The flaps of all four 
boxes were pasted over with white paper, but on the flap of the 
food box a small round black dise was stuck in the centre. 
Here again it was observed that it was comparatively easy by 
hanging the flap with the black food-token before another box each 
time, to teach the siskin, to look for its food exclusively behind 
the flap with the black disc. 
1) In fact the bird had by no means forgotten the first learned token of locality. 
| will revert to this point in the exhaustive paper to be issued soon. For the rest, 
experiments were frequently made with blank specimen, (empty boxes), to prevent 
nse of smell interfering. 
+ %) As is known, birds according to Hess do not see spectral colours further 
than the line of demarcation between green and blue. The difference detected 
must therefore be due to a difference in the shade. 
