§4.7.17 Τῶν δʼ ὀστρακοδέρμων οὐκ ἔστι τὸ σῶμα πολυμερές.
7 The body of testaceans is not composed of many parts.
τούτου δʼ αἴτιον τὸ μόνιμον αὐτῶν εἶναι τὴν φύσιν· πολυμερέστερα γὰρ ἀναγκαῖον εἶναι τῶν ζῴων τὰ κινητικὰ διὰ τὸ εἶναι αὐτῶν πράξεις· ὀργάνων γὰρ δεῖται πλειόνων τὰ πλειόνων μετέχοντα κινήσεων.
The reason for this is that their nature is stationary; for it is necessary that those of animals that are locomotive are composed of more parts because of their having actions; for those participating in more movements stand in need of more organs.
§4.7.2τούτων δὲ τὰ μὲν ἀκίνητα πάμπαν ἐστί, τὰ δὲ μικρᾶς μετέχει κινήσεως· ἀλλʼ ἡ φύσις πρὸς σωτηρίαν αὐτοῖς τὴν τῶν ὀστράκων σκληρότητα περιέθηκεν.
And of these, some are altogether motionless, while others participate in a little movement; but nature has placed around them the hardness of shells for their preservation.
ἔστι δὲ τὰ μὲν μονόθυρα τὰ δὲ δίθυρα αὐτῶν, τὰ δὲ στρομβώδη, καθάπερ εἴρηται πρότερον· καὶ τούτων τὰ μὲν ἑλίκην ἔχοντα, οἷον κήρυκες, τὰ δὲ σφαιροειδῆ μόνον, καθάπερ τὸ τῶν ἐχίνων γένος.
And some of them are single-shelled, others bivalve, and others spiral, as was said before; and of these, some have a whorl, like trumpets, while others are only spherical, like the genus of sea urchins.
§4.7.3καὶ τῶν διθύρων τὰ μέν ἐστιν ἀναπτυκτά, 3 οἷον κτένες καὶ μύες (ἐπὶ θάτερα γὰρ συγκέκλεισται, ὥστε ἀνοέγεσθαι ἐπὶ θάτερα καὶ συγκλείεσθαι), τὰ δʼ ἐπʼ ἄμφω συμπέφυκεν, οἷον τὸ τῶν σωλήνων γένος.
And of the bivalves, some are capable of opening, 3 such as scallops and mussels (for they are joined together on one side, so as to open and shut on the other side), while others are grown together on both sides, such as the genus of razor-clams.
§4.7.4ἅπαντα δὲ τὰ ὀστρακόδερμα, κπεραθά 4 τὰ φυτά, κάτω τὴν κεφαλὴν ἔχει.
And all testaceans, just like 4 plants, have their head downward.
τούτου δʼ αἴτιον ὅτι κάτωθεν λαμβάνει τὴν τροφήν, ὥσπερ τὰ φυτὰ ταῖς ῥίζαις.
The reason for this is that they take their food from below, just as plants do with their roots.
συμβαίνει οὖν αὐτοῖς τὰ μὲν κάτω ἄνω ἔχειν, τὰ δʼ ἄνω κάτω.
It happens to them, therefore, to have those parts which are naturally below above, and those which are above below.
ἐν ὑμένι δʼ ἐστί, διʼ οὐ διηθεῖ τὸ πότιμον καὶ λαμβάνει τὴν τροφήν.
And the head is in a membrane, through which it filters what is drinkable and takes its food.
ἔχει δὲ κεφαλὴν μὲν πάντα, τὰ δὲ τοῦ σώματος μόρια παρὰ τὸ τῆς τροφῆς δεκτικὸν ἀνώνυμα τἆλλα.
And all have a head, but the other parts of the body, except that which is receptive of food, are nameless.