Cocoon scene

leading from

Dan's Original Alien Story

a) At the end of the story is a missing scene which appears to be well known to the public as the cocoon scene, in which Ripley finds Captain Dallas spun into a web in the hold of the Earthship, Brett and (and at one time) Parker have also been spun into cocoons which are in the process of metamorphosing into the very same type of egg found in the pyramid, thus completing the Alien's life cycle (Dan O'Bannon's Unseen Alien, Starburst 15, p42) .

b) The first containing Dallas appears to be woven from some fine, white, silk-like material, and it is slowly undulating. Another cocoon dangles from the ceiling, but this one looks a little different. It is smaller and darker, with a harder shell. In fact, it looks almost exactly like the spores in the tomb thus completing the Alien Life Cycle (Dan O'Bannon's online early Alien script.)

c) Echoes of ideas from "They Bite"
The cocoon seen borrows echoes of some ideas from Dan O'Bannon's earlier script "They Bite" which he wrote back in 1975. His his story, after the creatures of the story, a strange type of primitive insect that remained hidden from man through recorded history. After the insect devoured its prey, it dissolved the prey in its highly specialised digestive juices, breaks it down to its molecular components and then copies the DNA patterns and grows a duplicate, except the duplicate is really an insect.This process involves a cocoon. The creatures are extremely specialised but mindless creatures that simply eat and reproduce and their ability to adapt is beyond belief, they can mimic anything.  

 Bug (1975) (source: http://en.wikipedia.org/)

d) Bug (1975)
Incidentally 1975 was the year that the movie Bug was released which was about an underground form of fire starting cockroach that couldn't live in surface air pressure for very long that came to the surface when a large crack in the ground develops after an earthquake and so the main character cross breeds it with a cockroach that lived on a surface, unleashing havoc.

 Bug (1975) (source: www.notrecinema.com)

Sources quotes:

1. At the end of the story is a missing scene which appears to be well known to the public as the cocoon scene, in which Ripley finds Captain Dallas spun into a web in the hold of the Earthship, Brett and (and at one time) Parker have also been spun into cocoons which are in the process of metamorphosing into the very same type of egg found in the pyramid, thus completing the Alien's life cycle (Dan O'Bannon's Unseen Alien, Starburst 15, p42) .
2. Phobos: Could you tell us a bit about the story
   Dan O'Bannon: Well, it's based on a freak of evolution, a primitive insect which branched off early from evolutionary lines of other insects. Its life cycle is so peculiar that it remains hidden from Man through all recorded history. Naturally, my script deals with their re-emergence in modern times. You see, they eat anything organic, animals, people, wood, plastic... and then they mimic the thing that they've eaten
   Phobos: Does it mimic it physically or spin a cocoon or something
   Dan O'Bannon: Basically a cocoon. After the insect has devoured its prey, it dissolves the prey in its highly specialised digestive juices, breaks it down to its molecular components, and then copies the DNA patterns and grows a duplicate... except the duplicate is really an insect. They're extremely specialized creatures. All they do is eat and reproduce. No minds. But they are adaptive beyond belief... they can mimic anything. And they run around eating everything. It's a structured as a horror story but I think it's fairly sophisticated. (Phobos No. 1 Summer 1977 (many thanks to DUNE ⟡ MdC & TΛU))