The metanephric cap is formed by the condensation of metanephric mesenchymal cells surrounding the ureteric bud tip[GO]. Mesenchyme closely apposed to the tips of the buds is called cap mesenchyme; it will later go on to form nephrons etc[GUDMAP]. [ http://www.gudmap.org/About/Tutorial/DevMUS.html#DMK_Nephron http://amigo.geneontology.org/amigo/term/GO:0072185 ]