Are the nodes of ranvier spaced equally along the axon? why is this significant?

Yes,  the nodes of Ranvier spaced equally along the axon to allow the action potential at first node to cause depolarization of second node.

Explanation:

Yes, nodes of Ranvier are equally spaced along the length of the axon. When an action potential reaches the first node, it generates the ionic movement in the cytosol and extracellular fluid so as to depolarize the membrane up to the threshold at the second node. This opens the voltage-gated Na+ channels at the second node to allow the ions to flow followed by generation of an action potential at the second node.  

Now, as the action potential is generated at the second node, the stimulated ionic movement opens the voltage-gated Na+ ion channels at the third node and the process is repeated. Hence, equally spaced nodes of Ranvier ensure that the action potential at one node can stimulate the depolarization at the next node.  

clumped distribution, because you'de have all of the population gathered in a relatively small are.

it's the most common because it provides protection and a mate for reproduction

example: humans, seeweed, cattles, etc.

he forelimbs below belong to four species that descended in a direct line from the ancestral mammal shown above. of the four descendants shown, which species most likely appeared earliest in evolutionary history?