1. Authorities have differed regarding the optimum degree of moisture associated with the presence of Collembola. Experiments have, therefore, been carried out to ascertain the influence of variation in relative humidity on the death-rate of certain species of these insects.

2. At a uniform temperature of 25° C. it was found that saturated conditions of the environment are necessary for the survival of all species of Collembola used in the experiments.

3. It has been found that, with the exception of the genus Entomobrya, Collembola devoid of a tracheal system are very susceptible to dry conditions. Sminthurus viridis, which possesses a tracheal system and well-developed ventral tube, is much less susceptible to atmospheric dryness.

4. An experiment carried out with Sminthurus mridis suggests that the ventral tube is used for conveying droplets of water from the hairs of the body to the mouth. It also serves as a "cleaning" organ.

5. The results of the above experiments have had direct practical application in methods of control of Collembola.

Now Adviser in Agricultural Zoology, University College of N. Wales.