his fair sister > (The moon: Phoebe (Diana) is the twin sister of Phoebus Apollo)
4 Ministers matter fit, which, tempered right
Ministers > Manages; furnishes; dispenses (Spenser's chief source for this account of spontaneous generation is Met. 1.416-37)
5 With heat and humour, breeds the living wight.
humour > moisture wight > creature
6 So sprang these twins in womb of Chrysogone, 7 Yet wist she naught thereof, but sore affright,
Yet wist she naught thereof, but sore affright > (Two inter- pretations seem possible: (1) "Yet knew she nothing thereof, but, sorely terrified," in which case "Wondered" at the start of line 8 means "Marvelled"; and (2) "Yet she knew nothing thereof but sore terror," giving "Wondered" the meaning "Filled with wonder")
8 Wondered to see her belly so up-blown,
up-blown > swollen
9 Which still increased, till she her term had full outgone.