1. Stauffer compound No. R-20458.
2. Both compounds were kindly supplied by F. Hoffmann-La Roche, Ltd., Basel.
3. Results presented to members of the A.R.C. Unit of Invertebrate Chemistry and Physiology at Brighton (Prof.A. W. Johnson, Director) and Cambridge (Dr.J. E. Treherne, Deputy Director) on March 19 and 20, 1973.
4. L. M. Riddiford, Biol. Bull.142, 310 (1972).
5. K. G. Davey, Int. J. Parasit.1, 61 (1971).