1. Trapping experiments were made to investigate the activity of cockroaches in a naturally infested animal room.

2. Under normal conditions of illumination (light by day and dark by night), activity only occurred at night, and most activity occurred during the period just before midnight. There was little activity during the later hours of darkness.

3. Artificial illumination of the order of 6 m.c. almost entirely prevented the cockroaches from appearing. Even lower intensities of light greatly reduced the number which appeared.

4. Darkening the room during the day did not cause the cockroaches to appear, unless the room had been artifically illuminated during the previous night.

5. Mechanical vibration and air movements appear to have little effect on the rhythmic activity of the cockroach.

6. The rhythmic activity of the cockroach appears to be controlled by some internal mechanism which we do not yet understand. External factors like light can modify the rhythm and may temporarily abolish it, but under normal conditions it is readily re-established.

Sorby Research Fellow of the Royal Society