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Male and female flour beetles are described in terms of one mortality characteristic: adult age at death. Four strains of Triboliurn ccnfusum and four strains of Tribolium castaneum were studied. The actual data are reported in two Appendix tables. Death rates were found to depend upon the species, strain, sex, and age of the individuals concerned. Differences between the mortality patterns of the two sexes were especially striking and seemed to have a common character for all strains and both species.

An earlier study (Park, I948), devoted to an experimental analysis of competition between two species of flour beetles (Tribolium confusum Duval and T. castaneum Herbst), led to the following major conclusions: (i) As single species populations ('controls') both T. confusum and T. castaneum maintained themselves successfully for essentially a 4-year period under the prevailing conditions of husbandry. (2) There were notable differences of species rank between the census curves of the control cultures. In other words, although both Tribolium were successful, the population growth-form of T. confusum differed significantly in pattern and mean density from that of T. castaneum. (3) When the two species were cultured together ('experimentals'), i.e. when a state of interspecies competition existed, one species invariably became extinct in response to this pressure of competition and the other species persisted. Of 74 replicates, T. confusum became extinct in 8 instances and T. castaneum in 66. (4) Knowing that both species of beetles were infected with a sporozoan parasite Adelina tribolii, and, wishing to evaluate the relation of such infection to their population behaviour, a series of cultures, both control and experimental, was established in which the parasite had been eliminated by manipulative means. The principal findings were these: (a) Non-parasitized populations of T. confusum behaved like parasitized populations in terms of density and pattern of growth, the only difference

I should not think it necessary before this audience to dwell at length upon the biological reality of the population. Just as the morphologist and physiologist concern themselves with the cell and organism as structural and functional units, so, it seems to me, the ecologist centers his attention around the population. There is nothing esoteric or paradoxical in this viewpoint. Certain resemblances between cell, organism and population emphasize the common properties of these three entities, while, at the same time, the possession by the population of other characteristics stresses its biological uniqueness. lt is these characteristics that give the population its individuality and make it so important from the point of view of the modern biologist; sufficiently so, apart from other possible considerations, to justify the existence of ecology.