function transferFrom(address _from, address _to, uint256 _value) {
        var _allowance = allowed[_from][msg.sender];
        
        migration (msg.sender);
        
        
        
        balances[_to] = balances[_to].add(_value);
        balances[_from] = balances[_from].sub(_value);
        allowed[_from][msg.sender] = _allowance.sub(_value);
        Transfer(_from, _to, _value);
    }