Como foi explicado na Wikipédia da Xenopedia :
Eggmorphing was originally to be witnessed during the climax of Alien, when Ripley discovers Dallas and Brett cocooned in the Nostromo's hold, with Brett being transformed into an Egg. The entire sequence was cut as director Ridley Scott felt it slowed down the final act of the film. However, the scene did appear in the movie's novelization, and was referenced in the novelizations of the sequel films.
Como fonte para esta explicação, a wikia refere-se a The Alien Legacy :
The Alien Legacy is a 1999 making-of documentary directed by Michael Matessino that details the production of the 1979 film Alien. Created for the Alien Legacy DVD box set, it uses interviews with the film's crew, as well as behind the scenes images and clips, to detail the development, filming and release of the movie.
A parte relevante está na parte "Alien on Board":
The seventh and longest chapter goes into the filming of the titular creature, in particular focussing on the infamous Chestburster scene and the decision to show as little of the Alien as possible throughout the film. Notably, the documentary also shows the deleted Eggmorphing scene almost in its entirety.