respectively depicted therein reference will be made herein to the prosthesis being endovascular although as pointed out above the prosthesis may be used in other applications in each embodiment the endovascular prosthesis 10 includes a tubular member 12 12 a and an outer covering 14 the tubular member 12 12 a is impervious to the transmission therethrough of a pre determined fluid particularly an occluding fluid while the outer covering 14 is pervious to the transmission therethrough of the pre determined fluid accordingly the prosthesis 10 can be utilized to at least partially occlude the sac of an aneurysm as described below the endovascular prosthesis 10 may take any shape or form as required although commonly the prosthesis 10 will have a cylindrical shape as shown in fig2 or a bifurcated y shape as shown in fig4 although only these two shapes are shown other shapes are possible the tubular member 12 12 a may be of any endovascular prosthetic construction known in the prior art including graft and stent graft configurations with reference to fig3 in the first embodiment the tubular member 12 has a cylindrical shape with a tubular wall 16 having an outer surface 18 and an inner surface 20 defining a single lumen 22 the tubular member 12 need not be formed as a right cylinder and may be irregularly formed e g bent eccentric in a second embodiment as shown in fig5 the tubular member 12 a has a bifurcated y shape with a first tubular portion 16 a defining a lumen 22 a from which extend branches 24 a 24 b each defining a lumen 26 in fluid communication with the lumen 22 a as is.