1. Smith, H. M., Science, 82, 151 (1935).
2. Buck, J. B., Quart. Rev. Biol., 13, 301 (1938).
3. We thank the American Philosophical Society and National Geographic Society for travel grants, and Professor Kloom Vajropala and Dr. Boonsong Lekagul for help in Thailand during 1965, October 11–20.
4. We thank Messrs. John Dunsmore, John Turner, R. B. Jagat and Peter Ashton for innumerable favours and extensive assistance in Sarawak during September 25–October 1, 1965.
5. Buck, J., and Buck, E., Science (in the press).