Sentence:  The <WSD>illapſe</WSD> of some pre-existent or animating formative Principle, which we may well call the Soul or "Anima", that as in the Generation of Mankind by ordinary procreation we ſee the formative power is ſome refined active Spirit or Soul "in ſemine deliteſcens", that faſhions the Matter, and actuates it with vital ſenſible Faculties and Operations; ſo the <WSD>illapſe</WSD> of ſome ſuch active ſubſtance or powerful Being, illapſing into Matter and uniting with it, might form it into that conſtitution which it enjoyed. 
Meaning of the word marked with <WSD> tags:  A gliding in; an immission or entrance of one thing into another.