Interlocking discs and hand-to-hand transfer

When choosing materials for our new baby the interlocking dics were high on my list. Why? Well they are so uniquely Montessori, I wanted to give them a try. I had not seen them used before and didn't know anyone who had used them. This certainly isn't the kind of material you find in your local baby shop. 

I presented the interlocking to discs to Otis when he was around three months old. He was grasping lots of things but stuggled with the discs. The things he liked to grasp were items he could get his fingers all the way around like rattles and the bars on his bell and ball cylinder.

It was the bell cylinder that he started with hand to hand transfer, the would hold the cylinder with two hands then let go with one hand, then hold with two and then let go with the other. However it is only now at four months that he has enough hand/finger strength to hold the discs and now completes this hand to hand transfer where he is actually passing the discs from hand to hand. 

The unique positioning of the discs means this hand to hand transfer also requires some wrist rotation. I think it was Nienhuis that said "through this transfer he creates different experiences with the same object".

There are many things that say Montessori and this is one of them.

Does anyone know the history of the interlocking discs? Please? Once again I am unhappy with just using a material but want to find out more about it. Who? When? Why?