The original answer may consist of motions to transfer venue, pleas to the jurisdiction, in abatement, or any other dilatory pleas; of special exceptions, of general denial, and any defense by way of avoidance or estoppel, and it may present a cross-action, which to that extent will place defendant in the attitude of a plaintiff. Matters in avoidance and estoppel may be stated together, or in several special pleas, each presenting a distinct defense, and numbered so as to admit of separate issues to be formed on them.