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As far back as 1678 Martin Lister, in his Historiæ Animalium Tractatus, has noted that, in the case of certain Molluscs, the fæces are of a regular form, and that their shape differs according to the species; he deduces from this that the intestine must show a corresponding difference in the various species.
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Hilary B. Moore (1933) studied this question.
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