fig1 a , 1b , and 1c show side - view partial cross - sections ( or cutaways ) of highly desirable variations of the inventive coil ( 100 , 200 , 210 ). the variations shown in fig1 a and 1b are made up of a helically wound outer coil ( 102 , 202 ) having a first end ( 104 , 204 ) and a second end ( 106 , 206 ). we refer to this form as the as the &# 34 ; primary &# 34 ; winding or shape . these variations include a stretch - resisting member ( 108 , 208 , 214 ) which is shown to be fixedly attached both to the first end ( 104 , 204 ) and to the second end ( 106 , 206 ). in certain circumstances , it may be desirable to attach the stretch - resisting member ( 108 , 208 ) only to one of the two ends , to at least one site between the to ends , or to neither of the two ends . clearly , for attaining stretch resistance , the stretch resisting member must be attached to at least two points on the coil . the stretch - resisting member ( 108 ) of the variation shown in fig1 a is fibrous and desirably polymeric . it may be a thermoplastic or thermosetting and comprise a bundle of threads or a single filament melted onto , glued , or otherwise fixedly attached to the vaso - occlusive coil ( 100 ). in some instances , it may also be desirable to include one or more metallic strands in the stretch - resisting member ( 108 ) to provide stiffness or electrical conductance for specific applications . the stretch - resisting member ( 208 ) of the variation shown in fig1 b is a simple wire or &# 34 ; ribbon &# 34 ; which is soldered , brazed , glued , or otherwise fixedly attached to the first end ( 204 ), second end ( 206 ), or to the coil at one or more locations intermediate to those the ends . the variation shown in fig1 c includes a stretch - resisting member ( 214 ) which is comprised of a helically wound coil which is soldered , brazed , glued , or otherwise fixedly attached to the first end ( 204 ) or second end ( 206 ) or in one or more intermediate locations . the stretch - resisting member ( 214 ) in this configuration provides a greater measure of lateral flexibility than the wire variation ( 208 in fig1 b ). it may be wound in either the same direction as is the outer coil ( 202 ) or in the alternate direction . a modest drawback to this variation is that it will stretch more than the fig1 b variation when axially stressed . the materials used in constructing the vaso - occlusive coil ( 102 , 202 ) and the stretch resisting member ( 108 , 208 , 214 ) may be any of a wide variety of materials ; preferably , a radio - opaque material such as a metal or a polymer is used . suitable metals and alloys for the wire making up the primary coil ( 102 , 202 ) and the stretch - resisting member ( 108 , 208 , 214 ) include the platinum group metals , especially platinum , rhodium , palladium , rhenium , as well as tungsten , gold , silver , tantalum , and alloys of these metals . these metals have significant radio - opacity and in their alloys may be tailored to accomplish an appropriate blend of flexibility and stiffness . they are also largely biologically inert . highly preferred is a platinum / tungsten alloy , e . g ., 8 % tungsten and the remainder platinum . the ribbon or coil stretch - resisting members ( 208 , 214 ) may also be of any of a wide variety of stainless steels if some sacrifice of radio - opacity and flexibility may be tolerated . very desirable materials of construction , from a mechanical point of view , are materials which maintain their shape despite being subjected to high stress . certain &# 34 ; super - elastic alloys &# 34 ; include various nickel / titanium alloys ( 48 - 58 atomic % nickel and optionally containing modest amounts of iron ); copper / zinc alloys ( 38 - 42 weight % zinc ); copper / zinc alloys containing 1 - 10 weight % of beryllium , silicon , tin , aluminum , or gallium ; or nickel / aluminum alloys ( 36 - 38 atomic % aluminum ). particularly preferred are the alloys described in u . s . pat . nos . 3 , 174 , 851 ; 3 , 351 , 463 ; and 3 , 753 , 700 . especially preferred is the titanium / nickel alloy known as &# 34 ; nitinol &# 34 ;. these are very sturdy alloys which will tolerate significant flexing without deformation even when used as very small diameter wire . if a superelastic alloy such as nitinol is used in the device , the diameter of the coil wire may be significantly smaller than that used when the relatively more ductile platinum or platinum / tungsten alloy is used as the material of construction . the coils may be made of radiolucent fibers or polymers ( or metallic threads coated with radiolucent or radio - opaque fibers ) such as dacron ( polyester ), polyglycolic acid , polylactic acid , fluoropolymers ( polytetrafluoro - ethylene ), nylon ( polyamide ), or even silk . should a polymer be used as the major component of the vaso - occlusive coil member , it is desirably filled with some amount of a radio - opaque material such as powdered tantalum , powdered tungsten , bismuth oxide , barium sulfate , and the like . the coil material is first wound into a primary coil ( 102 , 202 ). the primary coil is typically linear after it has been wound . generally speaking , when the coil ( 102 , 202 ) is a metallic coil and that coil is a platinum alloy or a superelastic alloy such as nitinol , the diameter of the wire used in the production of the coil ( 102 , 202 ) will be in the range of 0 . 00025 and 0 . 006 inches . the wire is wound into a primary coil ( 102 , 202 ) having a primary diameter of between 0 . 003 and 0 . 025 inches . for most neurovascular indications , the preferable primary coil ( 102 , 202 ) diameter is 0 . 008 to 0 . 018 inches . we have generally found that the coil wire may be of sufficient diameter to provide a hoop strength to the resulting device sufficient to hold the device in place within the chosen body site , lumen or cavity , without substantially distending the wall of the site and without moving from the site as a result of the repetitive fluid pulsing found in the vascular system . the axial length of the primary coil will usually fall in the range of 0 . 5 to 100 cm , more usually 2 . 0 to 40 cm . depending upon usage , the coil may well have 10 - 75 turns per centimeter , preferably 10 - 40 turns per centimeter . all of the dimensions here are provided only as guidelines and are not critical to the invention . however , only dimensions suitable for use in occluding sites within the human body are included in the scope of this invention . once the primary coil ( 102 , 202 ) is wound , the stretch - resisting member ( 108 , 208 ) is inserted into the lumen of the primary coil ( 102 , 202 ) and secured to the coil as desired . ends ( 104 , 204 , 106 , 206 ) are preferably of the same diameter as is the primary coil ( 102 , 202 ). suitable polymeric materials for the polymeric stretch - resisting member ( 108 ) can be either thermosetting or thermoplastic . thermoplastics are preferred because they allow simplification of the procedure for constructing the device ( 100 ) since they may be melted and formed into the end or ends ( 104 , 106 ). simple devices such as soldering irons may be used to form the ends . thermosetting plastics would typically be held in place by an adhesive . suitable polymers include most biocompatible materials which may be made into fibers but include polyester such as polyethyleneterephthalate ( especially dacron ) and polyamides including the nylons , polyglycolic acid , polylactic acid , fluoropolymers ( polytetrafluoro - ethylene ), or even silk . especially preferred because of the long history of safe and effective usage in the human body is fibrous polyethyleneterephthalate ( pet ) sold as dacron . fig2 a shows a side - view partial cross - section of one end of inventive coil ( 100 ). fig2 a also shows the helically wound outer coil ( 102 ) having an end ( 106 ) which is formed from a formerly molten fiber which also makes up the stretch - resisting member ( 114 ). an end of this type may be considered to have modestly higher vaso - occluding properties than a metallic end . other functional equivalents to this structure include ends ( 106 ) formed of glues such as epoxies and their equivalents , and which are mechanical in nature . fig2 b shows an external knot ( 112 ) which fixes the length of the coil member ( 102 ) and keeps it from stretching ; fig2 c shows a reformed mass of formerly molten polymer or of glue which is of a diameter larger than the inner diameter of coil ( 102 ) and prevents the coil from stretching . the knot ( 112 ) and block ( 114 ) are not shown to be attached to the coil ( 102 ) but may be . the variations shown in fig1 a , 1b , 1c and 2a , 2b , and 2c are designed to be deployed by use of a pusher and a catheter in the manner discussed in ritchart et al , discussed above . other methods ( and concomitant fixtures or joints to accomplish those methods ) may also be used . for instance , the end of the device may be adapted to accept an electrolytically severable joint of the type discussed in u . s . pat . no . 5 , 354 , 295 and its parent , u . s . pat . no . 5 , 122 , 136 , both to guglielmi and sepetka , described above . fig3 a and 3b depict , in partial cross section , such variations . the vaso - occlusive coil ( 130 , 230 ) is attached to a fill member ( 132 , 232 ). the fill member ( 132 , 232 ) preferably comprises a thermoplastic formed into place or an epoxy or the like and adheres , in turn , both to the stretch resistant member ( 134 , 234 ) and the core wire ( 136 , 236 ). the core wire ( 136 , 236 ) in this variation has an enlarged member which is embedded in the fill member ( 132 , 232 ). the core wire ( 136 , 236 ) is insulated , typically with a combination of polytetrafluoroethylene and parylene ( polyparaxyxylene ), except for a small sacrificial joint ( 138 , 238 ) which is intended to be the site of the electrolysis as the joint ( 138 , 238 ) is eroded or severed and the coil deployed into the body site . the details of this variation ( sans stretch - resistant member ( 136 , 236 )) are discussed in gia et al , u . s . pat . application ser . no . 08 / 367 , 061 , filed dec . 30 , 1994 , the entirety of which is incorporated by reference . fig4 a shows still another variation of a joint for releasing the inventive coil into a site within the human body . in this instance , the joint is mechanically deployed . the primary coil ( 140 ) incorporates interlocking clasps , one ( 142 ) located on an end of the coil ( 140 ) and one ( 144 ) located on the end of a pusher ( 146 ). the stretch - resisting member ( 148 ) is attached to the interlocking clasp ( 142 ) via a filler block ( 154 ). again , the filler block ( 154 ) comprises a material ( e . g ., a thermoplastic or adhesive material ) which may be placed in the coil and will adhere to the stretch - resistant member ( 148 ). the coil assembly ( 150 ), made up of the primary coil ( 140 ), interlocking clasp ( 142 ), and stretch - resisting member ( 148 ) is deployed by retracting catheter body ( or sheath ) ( 152 ). fig4 b shows a variation of the device depicted in fig4 a which does not employ special filler block material ( 154 ) for adhering to the stretch - resistant member . other mechanically deployable joints suitable for use with the inventive coil are described in : u . s . pat . no . 5 , 234 , 437 , to sepetka , ( shows a method of unscrewing a helically wound coil from a pusher having interlocking surfaces ). u . s . pat . no . 5 , 250 , 071 , to palermo , ( shows an embolic coil assembly using interlocking clasps mounted both on the pusher and on the embolic coil ) u . s . pat . no . 5 , 261 , 916 , to engelson , ( shows a detachable pusher / vaso - occlusive coil assembly having an interlocking ball and keyway - type coupling ) u . s . pat . no . 5 , 304 , 195 , to twyford et al . ( shows a pusher - vaso - occlusive coil assembly having an affixed , proximally extending wire carrying a ball on its proximal end and a pusher having a similar end , which two ends are interlocked and disengage when expelled from the distal tip of the catheter ) u . s . pat . no . 5 , 312 , 415 , to palermo ( also shows a method for discharging numerous coils from a single pusher by use of a guidewire which has a section capable of interconnecting with the interior of the helically wound coil ). u . s . pat . no . 5 , 350 , 397 , to palermo et al . ( shows a pusher having a throat at its distal end and a pusher through its axis . the pusher sheath will hold onto the end of an embolic coil and will then be released upon pushing the axially placed pusher wire against the member found on the proximal end of the vaso - occlusive coil ). as was noted above , the devices of this invention may have the simple linear shape shown in fig1 and 2 or may have shapes which are not so simple . fig5 , and 7 show what are termed &# 34 ; secondary &# 34 ; shapes in that they are formed from the primary coil by the simple act of winding the primary coil on a form of a desired shape and then heat treating the so - formed shape . fig5 shows a &# 34 ; c &# 34 ; shaped coil assembly ( 160 ) having a stretch - resistant member ( 162 ). fig6 shows a clover - leaf shaped coil assembly ( 164 ) also having a stretch - resistant member ( 162 ). fig7 shows a double - loop coil assembly ( 166 ). these are indicative of the various secondary shapes suitable for this invention . additionally , these inventive devices may also be used in conjunction with various external fiber adjuncts . fig8 shows a partial side - view of a linear variation of the inventive device ( 170 ) having filamentary material ( 172 ) looping through the coil ( 174 ). this method of attachment is described in greater detail in u . s . pat . nos . 5 , 226 , 911 and 5 , 304 , 194 , to chee et al , the entirety of which are incorporated by reference . a further description of a desirable fiber attachment is shown in u . s . patent application ser . no . 08 / 265 , 188 , to mirigian et al , filed jun . 24 , 1994 . fig9 shows a partial cutaway of a device ( 180 ) having a braided covering ( 182 ) of a filamentary material and a stretch - resisting member ( 184 ). this method of enveloping a coil is described in greater detail in u . s . pat . nos . 5 , 382 , 259 , to phelps et al , the entirety of which is incorporated by reference . the fibrous woven or braided tubular materials may be made from a biocompatible materials such as dacron ( polyester ), polyglycolic acid , polylactic acid , fluoropolymers ( polytetrafluoroethylene ), nylon ( polyamide ), or silk . the strands forming the braid should be reasonably heavy , e . g ., having tensile strength of greater than about 0 . 15 pounds . the materials mentioned , to the extent that they are thermoplastics , may be melted or fused to the coils . alternatively , they may be glued or otherwise fastened to the coils . preferred materials are dacron . fig1 a - 10d depict a common deployment method for introduction of the inventive vaso - occlusive devices described here . it may be observed that these procedures are not significantly different than those described in the ritchart et al . patent mentioned above . specifically , fig1 a shows the distal tip of a delivery catheter ( 310 ) which is within the opening ( 312 ) of an aneurysm ( 314 ) found in an artery ( 316 ). the distal or end section of the vaso - occlusive device ( 318 ) is shown within the catheter ( 310 ). in fig1 b , the distal end portion of the vaso - occlusive device ( 318 ) has exited the distal end of the catheter ( 310 ) and has wound into a secondary shape within the aneurysm ( 314 ). fig1 c shows the completion of the formation of the secondary shape within the aneurysm ( 314 ). fig1 d shows the separation of the vaso - occlusive device ( 318 ) from the pusher , placement within the aneurysm ( 314 ), and the withdrawal of the catheter from the mouth of the aneurysm . once the inventive coil is in place in an aneurysm or other site , there may be an occasion during which the coil must be moved or even withdrawn . for instance , in fig1 d , the coil might extend through the mouth ( 312 ) of the aneurysm into the artery . occlusion would not be desirable in the artery . a device such as the endovascular snare shown in u . s . pat . no . 5 , 387 , 219 , to rappe , may then be used to grasp the exposed coil and move it or retrieve it from the body . the stretch - resisting member of this invention prevents the coil from stretching into a single strand of wire and multiplying in length . modification of the above - described variations of carrying out the invention that would be apparent to those of skill in the fields of medical device design generally , and vaso - occlusive devices specifically , are intended to be within the scope of the following claims .