Most animal species that have brains are organized bilaterally, ie in
two hemispheres.  Most species also are organized so that the left
hemisphere relates to the right side of the body and vice versa.  This
is referred to as cross-lateralisation.  This arrangemnt seems to have
been quite clearly selcted for in evolutionary terms, but I am unclear
as to what evolutionary advantage cross-lateralisation provides.  Are
there any species that show ipsi-lateral organisation?