(a and b) Examples of “spontaneous” crypt fission (bifurcation) in normal adult mouse small intestine. (c) Multiple fission after irradiation with 12 Gy. A new crypt can be seen developing from the mid-crypt region as well as from the crypt base. Each neocrypt contains Paneth’s cells. (d) Similar bifurcation from a higher crypt-cell position can be seen in the colon after irradiation (10 Gy).