Junction Field Effect Transistors (JFETs) are commonly used as a current source/sink.
Connecting the gate directly to the source provides the Idss, which is the maximum current through that particular JFET.
A resistor between the gate and source will lower the amount of current from the Idss.
JFETs come in N channel and P channel. The J310 is relatively common N channel JFET.
N channel gate arrow points into the component schematic, whereas the P channel JFET schematic symbol points out of the schematic symbol.