1. Enigk, K. & Friedhoff, K. Z. ParasitKde. 21, 238–256 (1962).
2. Garnham, P. C. C. & Bray, R. S. J. Protozool. 6, 352–355 (1959).
3. Fitzpatrick, J. E. P. et al. Nature 217, 861–862 (1968).
4. Gorenflot, A., Piette, M. & Marchand, A. Rec. Med. Vet. 152, 289–297 (1976).
5. Williams, H. & Lewis, D. Proc. 4th Int. Cong. Parasit., Warsaw (in the press).