You keep claiming that, yet you consistently fail to provide any evidence to support your position. Since you are so sure, please cite the definition of "sheath" which a continuous "tube" does NOT meet. Unless you can then you have no basis for your argument since it really comes down to "a sheath is something that has been officially called 'the sheath'" - which is somewhat at odds with what everyone except you understands as the meaning of "sheath".Interesting to note, though, that Simon understands as little about the discussion as watson does.