首楞嚴義疏注經 7.186

7.186

雜染即愛，愛名為欲，欲故生潤乃名為滋。橫竪者，人行正道竪首而行，違正因邪故生橫類。遏蒲曇，云疱胎卵分也。

Defilement is love; love is called desire; because of desire, moisture is generated, and this is called nourishment. As for 'horizontal and vertical,' humans practice the correct path and walk with their heads held vertically; those who contravene the correct and follow the deviant are born as the horizontal classes. 'Arbuda' means a vesicle, the stage where womb and egg diverge.