The phenomenon known as the secular polar motion is, in essence, a relative displacement of the mean pole of the epoch of observation and the Conventional International Origin (CIO). The latter is attached to the zeniths of the five international latitude stations. If the zeniths were fixed relative to one another, or, in the terminology of A. Danjon, formed an invariable constellation, then the CIO could be considered as fixed with respect to such a constellation. But this is not the case: displacements of zeniths with respect to one another do occur. The question is how large they are.