The peculiar disagreeable odor of the adult bed-bug is due to the secretion of the stink glands which lie on the inner surface of the mesosternum and open by a pair of orifices in front of the metacoxæ, near the middle line. In the nymphs, the thoracic glands are not developed but in the abdomen there are to be found three unpaired dorsal stink glands, which persist until the fifth molt, when they become atrophied and replaced by the thoracic glands. The nymphal glands occupy the median dorsal portion of the abdomen, opening by paired pores at the anterior margin of the fourth, fifth and sixth segments. The secretion is a clear, oily, volatile fluid, strongly acid in reaction. Similar glands are to be found in most of the Hemiptera-Heteroptera and their secretion is doubtless protective, through being disagreeable to the birds. In the bed-bug, as Marlatt points out, "it is probably an illustration of a very common phenomenon among animals, i.e., the persistence of a characteristic which is no longer of any special value to the possessor." In fact, its possession is a distinct disadvantage to the bed-bug, as the odor frequently reveals the presence of the bugs, before they are seen. The eggs of the bed-bug (fig. 70) are pearly white, oval in outline, about a millimeter long, and possess a small operculum or cap at one end, which is pushed off when the young hatches. They are laid intermittently, for a long period, in cracks and crevices of beds and furniture, under seams of mattresses, under loose wall paper, and similar places of concealment of the adult bugs. Girault (1905) observed a well-fed female deposit one hundred and eleven eggs during the sixty-one days that she was kept in captivity. She had apparently deposited some of her eggs before being captured.