The moon people have apparently stripped the dead caterpillar of meat, leaving a giant caterpillar skeleton behind. While caterpillars don't have skeletons, this is a space caterpillar so I guess its fine.
Kate and the Professor are given a self-guided tour of the Selenite city, where they discover a huge solar powered goo machine that generates oxygen... I guess its like a tree with extra steps. They also find the Selenites are taking their spaceship apart, which upsets them.