1. Boland, L. M., and Fried, B. (1984). Chemoattraction of normal and Echinostoma revolu tum-infected Helisoma trivolvis to romaine lettuce (Lactuca sativa longefolia). J. Parasi tol. 70:436–439.
2. Connell, J. H. (1980). Diversity and the coevolution of competitors, or the ghost of competition past. Oikos 35:131–138.
3. Connell, J. H. (1983). On the prevalence and relative importance of interspecific competi tion: evidence from field experiments. Am. Nat. 122:661–696.
4. Conner, E. F., and Simberloff, D. (1979). The assembly of species communities: chance or competition? Ecology 60:1132–1140.
5. Cort, W. W., Hussey, K. L. and Ameel, D. J. (1960). Seasonal fluctuations in larval trematode infections in Stagnicola emarginata angulata from Phragmites Rats on Douglas Lake. Proc. Helminthol. Soc. Wash. 27:11–13.