X-rays and ultraviolet radiations delay regeneration and division of Blepharisma undulans. Irradiated blepharisma which have not been cut divide once or twice fairly soon after the controls then they cease dividing for a period of time (stasis) which may last for many hours or even days. Once they recover from stasis they divide at a rate comparable to controls. Cut irradiated blepharisma on the other hand having to replace lost parts start to divide later than the uncut irradiated individuals but little if any stasis occurs. As a consequence although irradiated with the same dosage cut individuals recover a normal rate of division sooner than uncut ones.