492 PROCEEDINGS OF THE ACADEMY OF [Juiie^ 



the ants were freshly captured from a single wild nest. My first arti- 

 ficial nest was roofed with transparent glass, and is hereinafter referred 

 to as the white nest. The second nest was roofed with double panes of 

 indigo glass, transmitting no hght-rays lower in the spectrmn than 

 blue. The third nest was roofed with double panes of blue and purple 

 glass, transmitting no hght-rays lower than blue, and showing under 

 the spectroscope a very broad band of \dolet. As the ants in the second 

 and third nests behaved nearly ahke, I shall refer to these two nests as 

 the violet nests. The fourth nest was roofed with double panes of 

 orange glass, transmitting only red and green rays, and this nest is 

 referred to as the orange nest. The fifth, the dark nest, had an opaque 

 roofing. All the nests were kept on a table in the diffused dayhght that 

 entered a large window, underneath a gas-jet that burned several hours 

 at night. The temperature and the humidity were nearly ahke for 

 all the nests, and the same food was supphed to all on the same days. 

 There was never any communication between the nests. 



From the beginning, the ants in the white nest and in the violet nests 

 behaved ahke in their efforts to seek shelter from the hght-rays enter- 

 ing their respective abodes. At first they packed themselves into the 

 hallways, coming out only at night or in very cloudy days for food. 

 The ultra violet rays entering the white and the violet nests, were those 

 that drove the ants to shelter. These rays are invisible to the hmiian 

 eye, and are not shown by the spectroscope; but Forel's ants,^ Formica 

 sangvinea and Formica siihsericea, withdrew from the isolated ultra- 

 violet rays as from full dayhght. For the logic of my experiments the 

 isolation of the ultra-violet rays was not required. There is no doubt 

 that the ants instinctively withdrew from the ultra-violet rays, and 

 that they are indifferent to all the other hght-rays. My experiments 

 show that they become fearless of, but not insensible to, these ultra- 

 violet rays, the time required therefor being in direct ratio to the 

 intensity of the illumination from the ultra-violet rays. 



It was not until December, 1902, that my ants gave sign of having 

 ceased to fear these rays when in charge of the young. In the night 

 and in cloudy days they brought the inert young out to occupy the 

 sponges in the center of the compartments. Toward the end of Janu- 

 ary, 1903, the ants in the violet nests occupied the middle areas of their 



glass, so tinted as to exclude light-rays above blue in the spectrum, would con- 

 duce to the serenity of the ants and facilitate the study of their ways. Cleanli- 

 ness, the right degree of humidity, pure air and a varied diet presented in minute 

 quantities, enables the ants to live long and prosper in these nests. 



■* "Ueber die Empfindlichkeit der Ameisen fiir Ultra- violet t und Rontgen'sche 

 Stralen," Prof. A. Forel und Prof. H. Dufour, Zoologischcn Jahrbiichern, 1902. 



