Abstract
1. The mouse is more susceptible to infection than the rat.2. The male in both the rat and the mouse is more susceptible to infection than the female.3. The development of the worm is slower in the male rat than in the female. This relationship does not occur in the mouse.4. The ecological position of the adult parasite was different in the mouse and rat, the worms living further down the intestine in the rat.5. The effects of host species on infection of N. dubius are discussed.
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