Letter | Published:

Influence of sexual dimorphism on foetal and placental weights in the rat

Naturevolume 257pages6263 (1975) | Download Citation



THE male is heavier than the female in the adults of most mammalian species. This trend is apparent at birth in humans1 and in many other mammals including the sheep, goat, cow, rat and monkey2. Little is known however, of the developmental basis for these birth weight differences. We have found that, one day before birth, male rat foetuses are 5% heavier than female foetuses, yet there seems to be no difference in the weights of their placentae.

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  1. Department of Anatomy and Human Biology, University of Western Australia, Nedlands, 6009, Western Australia

    • N. W. BRUCE
    •  & N. NORMAN


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