ΠΕΡΙ ΠΟΡΕΙΑΣ ΖΩΙΩΝ704 a
I. Περὶ δὲ τῶν χρησίμων μορίων τοῖς ζῴοις 5πρὸς τὴν κίνησιν τὴν κατὰ τόπον ἐπισκεπτέον διὰ τίν᾿ αἰτίαν τοιοῦτόν ἐστιν ἕκαστον αὐτῶν καὶ τίνος ἕνεκεν ὑπάρχει αὐτοῖς, ἔτι δὲ περὶ τῶν διαφορῶν τῶν τε πρὸς ἄλληλα τοῖς τοῦ αὐτοῦ καὶ ἑνὸς ζῴου μορίοις, καὶ πρὸς τὰ τῶν ἄλλων τῶν τῷ γένει διαφόρων. πρῶτον δὲ λάβωμεν περὶ ὅσων ἐπισκεπτέον.10
Ἔστι δὲ πρῶτον μὲν πόσοις ἐλαχίστοις τὰ ζῷα κινεῖται σημείοις, ἔπειτα διὰ τί τὰ μὲν ἔναιμα τέτταρσι τὰ δ᾿ ἄναιμα πλείοσι, καὶ καθόλου δὲ διὰ τίν᾿ αἰτίαν τὰ μὲν ἄποδα τὰ δὲ δίποδα τὰ δὲ τετράποδα τὰ δὲ πολύποδα τῶν ζῴων ἐστί, καὶ διὰ τί πάντ᾿ ἀρτίους ἔχει τοὺς πόδας, ὅσαπερ ἔχει 15πόδας αὐτῶν· ὅλως δ᾿ οἷς κινεῖται σημείοις, ἄρτια ταῦτ᾿ ἐστίν.
Ἔτι δὲ διὰ τίν᾿ αἰτίαν ἄνθρωπος μὲν καὶ ὄρνις δίπους, οἱ δ᾿ ἰχθύες ἄποδές εἰσιν· καὶ τὰς κάμψεις ὅ τε ἄνθρωπος καὶ ὁ ὄρνις δίποδες ὄντες ἐναντίας ἔχουσι τῶν σκελῶν. ὁ μὲν γὰρ ἄνθρωπος ἐπὶ 20τὴν περιφέρειαν κάμπτει τὸ σκέλος, ὁ δ᾿ ὄρνις ἐπὶ τὸ κοῖλον. καὶ ὁ ἄνθρωπος αὐτὸς αὑτῷ
Progression of Animals
I. We must next discuss the parts which are useful to animals for their movement from place to place, and consider why each part is of the nature which it is, and why they possess them, and further the differences in the various parts of one and the same animal and in those of animals of different species compared with one another. We must first decide what questions we have to discuss.
One question is, what is the smallest number of points at which animals move; the next is, why red-blooded animals move at four points, while bloodless animals move at more than four; and, in general, why some animals are without feet, others biped, others quadrupeds, and others polypods, and why all that have feet at all have an even number of feet; and, in general, why the points at which movement is made are even in number.
We must further consider why a man and a bird are bipeds, while fishes are without feet; and why a man and a bird, being both bipeds, have opposite bendings of the legs. For a man bends his legs in a convex direction, a bird in a concave direction; and a man