Eliot's note for line 428

V. Pervigilium Veneris. Cf. Philomela in Parts II and III.

Commentator's note

428)  Quando fiam uti chelidon--O swallow swallow

99)  The change of Philomel, by the barbarous king
100)  So rudely forced; yet there the nightingale
101)  Filled all the desert with inviolable voice
102)  And still she cried, and still the world pursues,
103)  'Jug Jug' to dirty ears.

203)  Twit twit twit
204)  Jug jug jug jug jug jug
205)  So rudely forc'd.
206)  Tereu

Additionally, see also Part V line 356-357 :

356)   Where the hermit-thrush sings in the pine trees
357)   Drip drop drip drop drop drop drop

As mentioned for line 103 the "twit", "jug" and "tereu" lines were used by Elizabetian poets to represent the song of the nightingale. Tereu is a form of the name Tereus. See Ovid's The Story of Tereus, Procne, and Philomela or our synopsis of the Philomela myth by visiting line 99.