intermingle

To mix (things) together.

These representative species often meet and interlock; and as the one becomes rarer and rarer, the other becomes more and more frequent, till the one replaces the other. But if we compare these species where they intermingle, they are generally as absolutely distinct from each other in every detail of structure as are specimens taken from the metropolis inhabited by each.

To become mixed together.

At present, passenger and goods traffic intermingle, a factor which complicates operation.