What is this symbol?

I am trying to figure out what the symbol circled is in the attached schematic of a signal conditioner. I also do not understand why the wires for a gain of 10 and 100 end up in the same location but have different gains.

Any help would be appreciated as I am not an electrical engineer by training but an ocean engineer working on an circuit analysis for an underwater acoustics project.

That is a 2 mA constant current source.

Those aren't just wires for the gain. It's supposed to abbreviate a selectable gain set by voltage dividers. For a voltage gain in that setup, you would have two resistors connected to the inverting input of the op amp. One resistor would go to ground and the other resistor would go to the output of the op amp. For a gain of 10, the resistor connected to the output would have a resistance 9 times greater than the resistor connected to ground. For a gain of 100, the resistor connected to the output would have a resistance 99 times greater than the resistor connected to ground.