There is optionally the substitution of ā in the room of the diphthong of the root vī in the causative, when meaning 'to conceive an embryo'.,
The root वी Adadi 39 means 'to go, to conceive, to shine, to eat, and to desire'. The substitution takes place when it means 'to impregnate or conceive'. Thus पुरो वानो गाः प्रवापयति or प्रवाययति = गर्भे ग्राहयति ॥ The word प्रजन means the receiving of the embryo which in course of time will lead to the birth of a child.,