“I was watching tennis” is an example of the imperfect tense.

The cotton grower felt delight at the gainsome expansion of his cotton fields.

Germarium and vitellarium are distinct and the latter contains one or two small, immature basal oocytes.

… it settles the vexed question as to whether Stroudley or R. J. Billinton first introduced crescent-shaped balanceweights into the driving and coupled wheels of L.B. & S.C. locomotives.