Pygtk: how to pass your signals?

Question

GTK+

there are two children of EventBox. It is necessary to transmit a signal from one to another.
When initializing the receiver, on connect('message-send') I get an error - an unknown signal name: message-send
I read the dock on signals, read and tried tutorials on how to use signals. The example works, mine doesn't.
I reviewed a bunch of packs on github, I don’t understand what exactly is wrong with me.
It feels like I've missed something, but I can't figure out what it is.
source - pastebin.com/t9Kv92sZ