俱舍論疏 8.141

8.141

論「云何胎生至猪羊驢等」，釋胎生也。依胎而生名為胎生。有胎無卵，故在卵後說。為胎必濕，故濕生先說。

The Śāstra says: "What is womb-born? [...] pigs, sheep, donkeys, and so forth." This explains womb-born. That which is born relying on a womb is called womb-born. Having a womb without an egg, it is therefore spoken of after the egg-born. To form a womb it must have moisture; therefore, moisture-born is spoken of earlier.