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I then (July 15, 1876) laid the strips of glass on one of my nests of Formica fusca, containing about 170 ants. These ants, as I knew by many previous observations, seek darkness, at least when in the uest, and would collect in the darkest part. I then, after counting the ants under each strip, moved the glasses, at intervals of about half an hour, so that each should by turns cover the same portion of the nest. The results were as follows—the numbers indicating the approximate numbers of ants under each glass (there were sometimes a few not under any of the strips of glass):
Adding these numbers together, there were, in the twelve observations, under the red 890, under the green 544, under the yellow 495, and under the violet only 5. The difference between the red and the green is very striking, and would doubtless have been more so, but for the fact that when the colours were transposed the ants which had collected under the red sometimes remained quiet, as, for instance, in cases 7 and 8. Again, the difference between the green and yellow would have been still more marked but for the fact that the yellow always occupied the position last held by the red, while, on the other hand, the green had some advantage in coming next the violet. In considering the difference between the yellow and green, we must remember also that the green was decidedly more opaque than the yellow.
The case of the violet glass is more marked and more interesting. To our eyes the violet was as opaque as the red, more so than the green, and much more so than the yellow. Yet, as the numbers show, the ants had scarcely any tendency to congregate under it. There were nearly as many under the same area of the uncovered portion of the nest as under that shaded by the violet glass.
Lasius flavus also showed å marked avoidance of the violet glass.
I then experimented in the same way with a nest of Formica fusca, in which there were some pupa, which were generally collected in a single heap. I used glasses coloured dark yellow, dark green, light yellow, light green, red, violet, and dark purple. The colours were always in the preceding order, but, as before, their place over the nest was changed after every observation.
To our eyes the purple was almost black, the violet and dark green very dark and quite opaque; the pupæ could be dimly seen through the red, rather more clearly through the dark yellow and light green, while the light yellow were almost transparent. There were about 50 pupæ, and the light was the ordinary diffused daylight of summer.
These observations showed a marked preference for the greens and yellows. The pupe were 61 times under dark green, 3 under dark yellow, 3} under red, and once each under light yellow and light green, the violet and purple being altogether neglected.
I now tried the same ants under the same colours, but in the sun; and placed a shallow dish containing some 10 per cent. solution of alum sometimes over
he yellow, sometimes over the red. I also put four chicknesses of violet glass, so that it looked almost black.
Under these circumstances, the pupäe were placed under the red 7 times, dark yellow 5, once they were half under each, but never under the violet, purple, light yellow, dark or light green.
The following day I placed over the same nest, in the sun, dark green glass, dark red, and dark yellow. In nine observations the pupæ were carried three times under the red and nine times under the yellow.
I then tried a similar series of experiments with Lasius niger, using a nest in which were about 40 pupæ, which were generally collected in a single heap all together. As before, the glasses were moved in regular order after each experiment; and I arranged them so that the violet followed the red. As far, therefore, as position was concerned, this gave violet rather the best place. The glasses used were dark violet, dark red, dark green, and yellow, the yellow being distinctly the most transparent to our eyes. Experiment
Experiment 1. Pupæ under yellow. 8. Pupæ under green.
yellow. 11. 12.
i di inconi
Experiment 15. Pupæ under green. | 24. Pupæ under red. 16.
yellow. yellow. 26.
green. I now put two extra thicknesses of glass over the red and green. 33. Pupæ under red. 37. Pupæ under red.
red. 39. „ yellow. 36. „ yellow. | 40. „ red.
The result is very striking, and in accordance with the observations on Formica fusca. In 40 experiments the pupa were carried under the yellow 19 times, under the red 16 times, and under the green 5 times only, while the violet was quite neglected. After the first twenty observations, however, I removed it,
I then tried a nest of Cremastogaster scutellaris with violet glass, purple glass, and red, yellow, and green solutions, formed respectively with fuchsine, bichromate of potash, and chloride of copper. The purple looked almost black, the violet very dark; the