Consistency is not one of Dark Angel's strongest points. Case in point: the X7.

Initially, the X7 were clones of the X5--we were shown an X7 version of both Max and Zack in And Jesus Brought a Casserole. Max's clone made a final appearance in Designate This where we learned that she was suffering from late-state progeria--this was the first hint that there was something special about Max as her young clone's DNA was identical to Max's save for her X7-specific code sequences.

Past that point, the X5 clones ceased to be shown. Instead, the X7 became clones of one another--"many of one," as Joshua explained. They also gained distinctive black eyes.

The X7 had a hive mind and did not communicate through the spoken word. They communicated in the ultrasonic range ("Bat. Bat in their cocktail"). Their speech was in digital code which was downloaded into a computer that translated the ultrasonic signals.

Lydecker stated that the X7 were"stronger, faster" than the X5, and they were able to take out Max and Zack during the assault on Manticore. The X7 were used to patrol the woods around Manticore, and in the second season, Ames White's agency also used them to track down the escaped transgenics. We witnessed several X7s taking down a lizard transgenic in Bag 'Em. An X7 was also used to keep track of Max, Alec and the Bag 'Em kids in that episode.

Sometime after Bag 'Em, White and his agency most likely moved to eliminate the X7s as well, for there were X7s taking refuge in Terminal City with the other escaped transgenics.

Where to find X7: And Jesus Brought a Casserole, Designate This, Bag 'Em, and a very brief mention in Freak Nation.