Morphological discussion: genitive formations with -κος/-κτος give stems ending in -ξ (e.g. γάλακος→γάλαξ) and subsequent loss or reanalysis of -ξ (γάλα from γάλακτος); dative plural and stem alternations; examples of κρᾶτα, neuter -μα nouns, and related place names.
λίπας καὶ τὸ ὕφα ἐκ τοῦ ὕφασμα κατὰ ἀποκοπήν. καὶ τὸ γάλα ἀπὸ τοῦ γάλαξ κατ´ ἔνδειαν τοῦ 'ξ'. ἡ γὰρ κλίσις αὐτοῦ ἀπὸ εὐθείας τῆς εἰς 'ξ' καταληγούσης ἐγένετο· γάλακος γὰρ ἡ γενικὴ καὶ κατὰ πλεονασμὸν τοῦ 'τ' γάλακτος ὥσπερ ἄναξ ἄνακος καὶ ἄνακτος. πᾶσα γὰρ γενικὴ διὰ τοῦ 'κος' κλινομένη ἢ διὰ τοῦ 'κτος' τὴν εὐθεῖαν ἔχει εἰς 'ξ' καταλήγουσαν, οἷον Φοῖνιξ Φοίνικος, θώραξ θώρακος, νύξ νυκτός, ἄναξ ἄνακτος· εἰ οὖν γάλακτος, δῆλον ὅτι εἰς 'ξ' γάλαξ. ἄλλως τε δὲ πᾶσα δοτικὴ πληθυντικῶν εἰς 'ι' λήγουσα μετὰ διπλοῦ ἀποβολῇ τοῦ 'ι' τὴν εὐθεῖαν τῶν ἑνικῶν ἀποτελεῖ, οἷον Φοίνιξι Φοῖνιξ, κήρυξι κῆρυξ, Πέλοψι Πέλοψ, Κύκλωψι Κύκλωψ. εἰ οὖν ἐστιν ἡ δοτικὴ τῶν πληθυντικῶν γάλαξι, δῆλον ὅτι ἀποβολῇ τοῦ 'ι' γίνεται ἡ εὐθεῖα τῶν ἑνικῶν γάλαξ· ἀλλ´ ἐπειδὴ τὸ 'ξ' οὐκ ἔστι τελικὸν τῶν οὐδετέρων, τούτου χάριν ἀπεβλήθη καὶ ἐγένετο γάλα. Ἀμέλει συντιθέμενον τὸ γάλα καὶ γινόμενον εἰς ἀρσενικὸν γένος, ἀναδέχεται τὸ ὀφειλόμενον 'ξ' οἷον ὁ ἀρτιγάλαξ, ὁ νεογάλαξ. καὶ ἐκ τοῦ γάλαξ ὁ γαλαξίας γενέσθαι δοκεῖ. Περὶ δὲ τοῦ κρᾶτα οἷον »ἐς τὸ κείνου κρᾶτα ἐνήλαθ´ ἡ τύχη« παρὰ Σοφοκλεῖ (Oed. Tyr. 263) μήποτέ ἐστιν εἰπεῖν ὅτι τοῦτο ἀπὸ ἀρσενικοῦ ἢ θηλυκοῦ γέγονεν. ἀπὸ ἀρσενικοῦ μὲν ἀπὸ τοῦ ὁ κράς τοῦ κρατός τῷ κρατί τὸν κρᾶτα, ἀπὸ θηλυκοῦ δὲ ἀπὸ τοῦ ἡ κράς τῆς κρατός τῇ κρατί τὴν κρᾶτα καὶ τὸ κρᾶτα. τὸ μὲν γὰρ κράς ἀρσενικῶς καὶ θηλυκῶς λέγεται οἷον ὁ κράς καὶ ἡ κράς. Τὰ μὲν οὖν δισύλλαβα εἰς 'μα' λήγοντα οὐδέτερα παροξύνεται ἢ προπερισπᾶται, στόμα, πλύμα, ῥύμα, φύμα, θύμα, λύμα, θέμα, δέμα, ἅρμα—ἔστι καὶ πόλις Βοιωτίας τῆς Ταναγρικῆς. Παυσανίας ἐνάτῳ (c. 19, 4). ἐκλήθη δὲ οὕτως ἢ διότι ἐκεῖ κατεάγη τὸ τοῦ Ἀδράστου ἅρμα ἢ ἀπὸ Ἀμφιαράου τοῦ ἅρματος· ἐνταῦθα γὰρ καταφυγεῖν φασι μετὰ τοῦ ἅρματος καὶ οὐκ ἐκδοθῆναι τοῖς διώκουσιν ὑπὸ τῶν κατοικούντων. ἔστι καὶ τῆς Ἀττικῆς Ἅρμα ἐν Πάρνηθι περὶ τὴν Φυλὴν καλουμένην. ἔστι καὶ Ἅρματα πόλις πληθυντικῶς Ἰνδικῆς—αἷμα, βῆμα, ῥῆμα, χρῆμα, σῆμα, ὅθεν Κυνόσσημα τόπος Λιβύης. Ἑκαταῖος περιηγήσει αὐτῆς. ἔστι καὶ ἄλλο χωρίον. λῦμα καὶ φῦμα καὶ θῦμα παρ´ Ἀττικοῖς τὸ 'υ' ἐκτείνουσιν, ζεῦγμα καὶ Ζεῦγμα πόλις Συρίας
λίπας and ὕφα are from ὕφασμα by apocope. And γάλα is from γάλαξ by loss of the ‘ξ’. For its inflection arose from a nominative ending in ‘ξ’: the genitive is γάλακος, and with addition of ‘τ’, γάλακτος, just as ἄναξ, ἄνακος, and ἄνακτος. For every genitive inflected through -κος or through -κτος has a nominative ending in ‘ξ’, e.g. Φοῖνιξ, Φοίνικος; θώραξ, θώρακος; νύξ, νυκτός; ἄναξ, ἄνακτος. If, then, it is γάλακτος, it is clear that the nominative is γάλαξ ending in ‘ξ’. Moreover, every dative plural ending in ‘ι’, by dropping the ‘ι’ after a double consonant, produces the nominative singular, e.g. Φοίνιξι, Φοῖνιξ; κήρυξι, κῆρυξ; Πέλοψι, Πέλοψ; Κύκλωψι, Κύκλωψ. If, then, the dative plural is γάλαξι, it is clear that by dropping the ‘ι’ the nominative singular becomes γάλαξ; but since ‘ξ’ is not a final letter of neuters, for this reason it was dropped and γάλα resulted. Accordingly, when γάλα is compounded and becomes masculine in gender, it admits the required ‘ξ’, e.g. ὁ ἀρτιγάλαξ, ὁ νεογάλαξ. And from γάλαξ γαλαξίας seems to have been formed.
As for κρᾶτα, as in “ἐς τὸ κείνου κρᾶτα ἐνήλαθ᾽ ἡ τύχη” in Sophocles (Oed. Tyr. 263), perhaps one may say that this has come from a masculine or a feminine. From a masculine, from ὁ κρᾶς, τοῦ κρατός, τῷ κρατί, τὸν κρᾶτα; from a feminine, from ἡ κρᾶς, τῆς κρατός, τῇ κρατί, τὴν κρᾶτα, and τὸ κρᾶτα. For κρᾶς is said both in the masculine and in the feminine, e.g. ὁ κρᾶς and ἡ κρᾶς.
Now the disyllabic neuters ending in -μα are accented either with the acute on the penult or with the circumflex on the antepenult: στόμα, πλύμα, ῥῦμα, φῦμα, θῦμα, λύμα, θέμα, δέμα, ἅρμα—there is also a city of Boeotia in the Tanagran territory. Pausanias in the ninth book (c. 19, 4). And it was so called either because there the chariot of Adrastus was broken, or from the chariot of Amphiaraus; for there, they say, he took refuge with his chariot and was not handed over to his pursuers by the inhabitants. There is also in Attica Ἅρμα on Parnes near what is called Phyle. There is also Ἅρματα, a city in the plural, of India—αἷμα, βῆμα, ῥῆμα, χρῆμα, σῆμα, whence Κυνόσσημα, a place of Libya. Hecataeus in his description of it. There is also another locality. In λύμα and φῦμα and θῦμα among the Attic writers they lengthen the ‘υ’; ζεῦγμα, and Ζεῦγμα, a city of Syria.