首楞嚴義疏注經 4.110

4.110

In brief there are four modes of birth; in full there are twelve, as explained extensively below. When the four modes of birth arise, wherever karma corresponds with emotion and thought, birth is immediately undergone; hence it says "respond according to what is appropriate." Emotion, thought, union, and separation are possessed by all four modes of birth; here each is cited singly based on what is predominant, and the sūtra below naturally has greater or lesser amounts of emotion and thought. Furthermore, those born within eggshells are mostly due to thought, just as flying birds, fish, and dragons are all swift and agile; hence it says "born through thought." Those born within an embryonic womb have more emotion and less thought, because emotion is heavy and sinks down, unable to soar lightly; hence it says "exists on account of emotion." Those born in moisture do not rely on parents; simply their own emotion and thought unite with moisture, and they immediately undergo birth; hence it says "stimulated by union." Transformation is also from one's own thought longing for a superior realm, with emotional love for that object, and thereupon undergoes transformation birth; hence it says "responds by separation."