Joe Petagno, artist well known for his Motorhead album covers remembers being involved in the concept design process for the Facehugger when H R Giger was not around at Shepperton.Alien Explorations
Artwork revealed itself to be utilise the design that would be near enough be used in the final film but hisversion of the Facehugger on Kane’s face had a long penis like rod going down his throat to impregnate Kane with its offspring as would be seen in the x ray scan display
It was said that it was just the way writer Dan O’Bannon wanted it but Ridley Scott decided against it due to it being too explicit.
Dan was known to be not happy about the situation.
You can read and look at other information, images and designs at Alien Explorations.
I believe this design proves that the Pathogen also known as Plagiarus Praeportens is what the facehugger has always injected into the host.