Thanks for your question about muskmelon.  Here is a link with the reason that having more than one plant is recommended:

"Cucumbers, squash, pumpkin and watermelon have separate male and female flowers. Cantaloupe (muskmelon) has two flower types, male flowers and complete flowers (having both male and female parts). Cantaloupe flowers have a pollination window of one day. Pollen must be transferred from the male flower to the female flower on this day for seed set and fruit development. Fruit size and shape are related to the number of seeds set. Poorly pollinated flowers either abort or produce misshapen fruit."

I've attached a photo which has both the male and the female flowers, so you can see the difference.

Planting two plants doesn't guarantee that you will have melons produced, but it greatly improves your chances, both because of the increased number of flowers, and the chance the pollination 'window' will work.    BTW, if you want to take over the pollination work, here's a link explaining hand pollination.

Hope this is helpful.  Good luck!

Thanks for your quick and informative answer.

Welcome!