Where is the oscillator in the 555 chip provided here?
Keep in mind the schematic shown in the datasheet is probably not exact.  Think of it more as a conceptual description.

Q1-Q6 and Q7-Q10,Q12-Q13 are each differential inputs, the front ends of comparators.  Notice that one side of each comparator is brought out and the other is either at 1/3 or 2/3 of the supply.  Q15-16 is a current mirror.  The way it is hooked up it provides a lot of gain to the left comparator.  The stuff right of that is mostly logic to produce the right signal in the right cases and to control the discharge output.  The stuff way at the right is the main output pin driver.