What are manx cats?

I have recently gained all sorts of time to watch and wonder at two 5 month old (Manx I'm convinced) kittens named Pheobe and Sable. They are very, very, very.......... curious, dexterous, vocal and attatching. Love to be apart of every portion of every waking , sleeping, eating, playing activity. Need I say we love them and were wondering if there is a certain manneer of finding these kittens breed from a blood or procedural test? how can we tell if they are of a ???? breed inclusivlly?