Did you read the text?
They're ultrasonic microphones so it can't be a stereo amplfier, besides the schematic doesn't look like a stero amplifier.
T3 is a common emitter amplifier with U2 at its input, not output, which suggests that U2 is a microphone, not a speaker.
U1 is connected to the output of another common emitter amplifier (T2) which suggests it's a speaker but the text says it's a microphone.
The IC could be anything, I couldn't find the datasheet. How does it get its power supply? Via R2, R7 and P1? That doesn't make much sense, there again we don't know what the IC is.