σκληρὰ τὴν φύσιν ούσα, ἐν τοῖς ἔχουσιν ὀστᾶ· ἐν δὲ τοῖς μὴ ἕχουσι τὸ ἀνάλογον, οἷον ἐν τοῖς ἰχθύσι τοῖς μὲν ἄκανθα τοῖς δὲ χόνδρος.
De partibus animalium. Aristotle. ed. Bernhard Langkavel. United States. 2016.
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