A prefilled, two-constituent system is provided with first and second containers or barrels. The first barrel includes a first chamber having a dispensing end or delivery end. The delivery end defines a dispensing passage or delivery passage communicating through the delivery end to accommodate the dispensing of fluid from the first chamber. A movable seal or reciprocable stopper is slidably disposed in the first chamber, and a first constituent is provided in the first chamber between the delivery end and the stopper. A second container or barrel is sized to be disposed in the first barrel and has a discharge end defining a discharge passage communicating through the discharge end to accommodate the discharge of fluid from the second barrel. A plunger is slidably disposed within the second barrel. A liquid second constituent is provided in the second barrel between the discharge end and the plunger. The first barrel stopper and the second barrel discharge end are engageable directly or indirectly to cooperatively define a coupling accommodating the flow of the liquid second constituent from the second barrel into the first chamber of the first barrel as the second barrel moves outwardly relative to the first chamber.