I am trying to read Prior Probabilities (1968), by Edwin T. Jaynes.
In two sections he discusses mollusk-like qualities [of parameter spaces]:
The real problem, therefore, must be stated rather differently [than that of Jeffreys and Bayes]; we suggest that the proper question to ask is: "For which choice of parameters does a given form such as that of Bayes or Jeffreys apply?" Our parameter spaces seems[sic] to have a mollusk-like quality that prevents us from answering this, unless we can find a new principle that gives them a property of "rigidity".
Stated in this way, we recognize that problems of this type have already appeared and have been solved in other branches of mathematics. In Riemannian geometry and general relativity theory, we allow arbitrary continuous coordinate transformations; yet the property of rigidity is maintained by the concept of the invariant line element, which enables us to make statements of the definite geometrical and physical meaning independently of the choice of coordinates.
What does mollusk-like quality actually mean in this context?