The eggs hatch in six to ten days, the newly emerged nymphs being about 1.5 mm. in length and of a pale yellowish white color. They grow slowly, molting five times. At the last molt the mesathoracic wing pads appear, characteristic of the adult. The total length of the nymphal stage varies greatly, depending upon conditions of food supply, temperature and possibly other factors. Marlatt (1907) found under most favorable conditions a period averaging eight days between molting which, added to an equal egg period, gave a total of about seven weeks from egg to adult insect. Girault (1912) found the postembryonic period as low as twenty-nine days and as high as seventy days under apparently similar and normal conditions of food supply. Under optimum and normal conditions of food supply, beginning August 27, the average nymphal life was 69.9 days; average number of meals 8.75 and the molts 5. Under conditions allowing about half the normal food supply the average nymphal life was from 116.9 to 139 days. Nymphs starved from birth lived up to 42 days. We have kept unfed nymphs, of the first stage, alive in a bottle for 75 days. The interesting fact was brought out that under these conditions of minimum food supply there were sometimes six molts instead of the normal number. The adults are remarkable for their longevity, a factor which is of importance in considering the spread of the insect and methods of control. Dufour (1833) (not De Geer, as often stated) kept specimens for a year, in a closed vial, without food. This ability, coupled with their willingness to feed upon mice, bats, and other small mammals, and even upon birds, accounts for the long periods that deserted houses and camps may remain infested. There is no evidence that under such conditions they are able to subsist on the starch of the wall paper, juices of moistened wood, or the moisture in the accumulations of dust, as is often stated. There are three or four generations a year, as Girault's breeding experiments have conclusively shown. He found that the bed-bug does not hibernate where the conditions are such as to allow it to breed and that breeding is continuous unless interrupted by the lack of food or, during the winter, by low temperature.