“…In addition, for the formation of various structures during morphogenesis, cell death occurs according to precise temporal sequences and spatial patterns and is considered to play a key role by elim- inating unnecessary cells to achieve complex histogenesis and organogenesis. For example, cell death is involved in remodeling the embryonic tail bud in humans (Kunimoto, 1918;Wittman et al, 1972;Fallon and Simandl, 1978), mice (Wittman et al, 1972;Schoenwolf, 1984;Tam, 1984), rats (Butcher, 1929;Gajović et al, 1989Gajović et al, , 1993Qi et al, 2000b), and chicks (Klika and Jelinik, 1969;Van Horn, 1971;Schoenwolf, 1981;Sanders et al, 1986;Mills and Bellairs, 1989;Miller and Briglin, 1996). Several investigators have indicated that cell death is involved in removal of the tailgut in chicks (Van Horn, 1971), rats (Š vajger et al, 1985), and humans (Fallon and Simandl, 1978).…”