Dude. The alien in alien 3 shed its chestburster skin ONCE. that's it, before murphey has acid spat in his face he finds the alien skin on the floor and picks it up. The events that took place on fury 161 happened over the course of a few nights, the alien was still young which is why it had its domed head, the aliens in the second movie on LV4-26 had been there (according to back story) around 2 - 3 weeks and had matured into fully developed adults. Like i said, there has to be reasoning for the change in the aliens during the ACTUAL movies, we ALL know that there were different designers, but as i said before, ripley is not going to turn to Bishop in aliens and say, "ooo look bishop these aliens look different to the first one i saw, it must be a special james cameron alien" THERE HAS TO BE A BACK STORY AND LOGICAL EXPLANATION FOR CHANGES WITHIN A MOVIE IF IT HAS SPAWNED SEQUELS THAT SHOW DIFFERENCES IN A RECOGNIZED CHARACTER.
These theories are covered in so many alien biology sites, you should try reading them, they make an incredible amount of sense. Put it this way, you can't have a movie franchise centered around a main character and change him in every movie without having an explanation in the movie for why he changed, it would make absolutely no sense at all, hence, the biological explanation for the change of the aliens to cover up the fact that the directors had changed the look of the aliens, its called 'keeping the fans happy'
The xenomorph in the third film didn't have the tubing on its back due to the adaption of DNA sampled from the dog (taking into account the theatrical cut of the film) The filteration tubing would have interfered with the creatures quadrupedal movement.
You don't have to appologise after your posts dude, but i think you will put alot of people's noses out of joint with those sort of opinions. Remember, the key to the facts i've given above is that they actually make sense, they were thought up for the purposes of covering up the change of design so they fans could have something legible to sink their teeth into. How boring would it be if there was no explanation, and secondly it would be damn right ridiculous.
Another example. Imagine superman, one film he's flying along, saving people with all his special powers then in the next film, a director changes everything about him. Superman no longer has super speed, he cant fly etc, but there's no explanation, people just say "oh well, it's because there's a different director" you cant just change things without having a story or explanation, it ruins the continuity of the whole saga.
www.thorndesigns.netdarkness of acheron