1. P. A. Guerette and J. M. Gosline, Department of Zoology, University of British Columbia, 6270 University Boulevard, Vancouver, British Columbia V6T 1Z4, Canada.
2. D. G. Ginzinger and B. H. F. Weber, Department of Medical Genetics, University of British Columbia, 2125 East Mall, Vancouver, British Columbia V6T 1Z4, Canada.