Delayed involution in BLG–Cre/Stat3flox/− mammary glands. (A,C,E,G) BLG–Cre/Stat3flox/+ mammary glands; (B,D,F,H) BLG–Cre/Stat3flox/− mammary glands; (A,B) day 10 of lactation; (C,D) day 2 of involution; (E,F) day 3 of involution; (G,H) day 6 of involution. Scale bar, 100 μm.