442 PROCEEDINGS OF THE AMERICAN ACADEMY. 



see that its presence makes any difference in the behavior of the ant 

 after the first few minutes, and the number of individuals which can 

 be thus marked is practically unlimited, for by varying the single or 

 combined colors, many different combinations can be secured. 



2. Heating. — In carrying out this set of observations the ants were 

 kept during the summer at ordinary room temperature. In winter, 

 however, in order to maintain a state of greater activity than they 

 would have had at room temperature, especially at night, it was deemed 

 expedient to keep them at temperatures which approximated those of 

 summer, the extremes being about 60'^ and 90° Farenheit. They were 

 therefore placed, when not under observation, in an artificially heated 

 chamber (Figure 5). This chamber, made of matched boards | in. thick, 

 was about five feet high, three and a half feet wide, and two and a 

 half feet from front to back, and raised on wooden legs about two feet 

 above the floor. The front of the chamber was composed of two doors 

 (c), and the back was open, but was placed against the wall of the 

 room in such a way as to surround a west window that was provided 

 with two sashes enclosing an air space between them. The floor, the 

 roof, the two ends and the two doors were lined with sheets of asbestos. 

 To give more surface on which to place the nests and to allow at the 

 same time free circulation of the heated air, a shelf (ci) made of slats 

 was placed midway between the floor and roof. Since the afternoon 

 sun sometimes made the temperature in the chamber dangerously high, 

 and since daylight excites ants, the window was supplied with a red 

 curtain {h), so arranged that it could be easily raised or lowered. The 

 curtain was used continuously except occasionally for a few moments 

 when a little extra light was needed while caring for the ants. Al- 

 though the doors could be tightly closed, they were usually left slightly 

 ajar, thus affording better ventilation and avoiding danger of too great 

 a rise of temperature. Heat was supplied by an electric stove {d), the 

 current being taken from the lighting circuit. The ants which I was 

 studying were kept on the floor of the chamber, where the temperature 

 was somewhat lower than on the shelf The latter was used by Mr. I. 

 A. Field for the ants he was rearing in connection with his studies on 

 spermatogenesis. The chamber was built for receiving ants and in 

 accordance with plans worked out by Mr. Field and the director of the 

 laboratory. While the ants were kept in this chamber at such times 

 as they were not under immediate inspection, all observations were 

 made at ordinary room temperatures, under the influence of daylight. 



