Just to add to what Kchriste said, think of the ground symbol from two standpoints; one, to simplify the schematic, it is an implied connection to all other ground symbols without explict lines drawn, and two, think of it as "0V".
btw: lots of older opamps (LM111 is a special type of opamp called a comparator) utilize split power supplies, which are really two supplies sharing a common tie point which is tied to the ground of the opamp circuit, even though the opamp IC does not have a ground pin itself. Newer CMOS (especially rail-to-rail) OpAmps typically only use a single supply.