Fill in all the gaps, then press "Check" to check your answers. Use the "Hint" button to get a free letter if an answer is giving you trouble. You can also click on the "[?]" button to get a clue. Note that you will lose points if you ask for hints or clues!

In arthropods the of the
exoskeleton the passage of
difficult. In addition new
methods of present in
arthropods preserved by evolution
they were more for
those animals.