A fluid delivery injector comprises a syringe defining a barrel； a plunger and a hollow needle provided within the barrel adapted for linear movement parallel to a longitudinal axis with a distal tip of the needle contained within the syringe. A fluid retention reservoir is defined at least in the barrel and is in fluid communication with the needle when pressure is applied to the fluid in the reservoir and to the plunger for moving the needle out of the barrel. A spring may be provided for retracting the needle when pressure is released from the plunger.
