Abstract
A viscous secretion accumulates on the 6th and 7th tergites and the dorsal surface of cerci in both nymphs of Periplaneta fuliginosa and P. japonica when they are reared alone or in a low population density per container. It was scarcely found in the nymph of P. americana and not in adults of any of these 3 species. The nymphs of the former tow species with viscous secretion exhibited an active and characteristic defensive behavior against aggressive ants of Formica exsecta fukaii. This was found to be a means of splashing droplets of the secretion over some distance, making ants hepless instantly. On the other hand, the nymph of P. americana which has no or little secretion did not exhibit such a behavior, and was attacked and seriously injured by the ants.The viscous secretion consists principally of a protein, low or lacking in sulfur, and contains no noxious component. The dorsal glands had no relation to the secretion. The soruce of the secretion seemed to be the hypodermal cells corresponding to the viscous regions since the painting of each of them with bond completely prevented its accumulation. On these secretory regions, there were found a number of peculiar stout hairs.
