A study of the observations made on the development and, in some cases, even the decay of 15 large active regions is presented. It is shown that the mature spots results from the subphotospherically controlled attraction of several large fragments of 1-2 x 10 to the 21st Mx, which are themselves made of smaller elements. The fragments are more stable structures than the spots they constitute; and usually survive after the spot decay. In the process of coalescence of fragments to form the spot, the fusion is never complete and properly exposed photographs reveal light bridges or saddlelike distributions of umbral dots in the interstices between fragments. These are also the regions along which the breakup of the spot occurs. These observations fit within the expectations of the penetrative convection mechanism for umbral dots proposed by Parker (1979).