12 to bias piston 20 forward or toward the open end of cylinder 11 annular flap type seal 24 is mounted to piston 20 at the front thereof and is self biased against the interior wall of cylinder 11 with slide 14 in its normal inactive position shown in fig6 the check valve action of flexible slide 14 seals aperture 17 so that forward movement of piston 20 under the influence of spring 21 will be resisted by creation of a reduced pressure or vacuum condition within expandable chamber 29 that is formed within cylinder 11 between closure cap 12 and the rear of piston 20 to commence the birthing process utilizing its projection 89 slide 14 is moved to the left with respect to fig6 until engaging stop 95 now metering orifice 18 is aligned with aperture 17 so that air may bleed into chamber 29 to raise the pressure therein thereby reducing the vacuum force acting in opposition to the force of biasing spring 21 this permits piston 20 to move forward and force fetal dolls 39 within cylinder 11 through opening 27 as in the embodiment of fig1 3c even though air is permitted to bleed into expandable chamber 29 the rate at which this occurs is so low that forward movement of piston 20 is retarded.