The effort to control the “white fly” of the orange (Aleurodes citri) by hydrocyanic acid gas, naturally suggested an inquiry into the respiration of these insects. The author was enabred to pursue this inquiry, while recently in Florida, under the auspices of trre Florida Agricultural Experiment Station.The only account of the organs of respiration in the young of this family is a brief note with a figure in Burmeister's Handbuch, which is very incomplete and not entirely accurate. Some very interesting and quite unique features are presented by these insects, not the least of which are the breathing folds, that are very conspicuous structures, and have been heretofore incorrectly interpreted. The view suggested by Riley and Howard (Insect Life, 1893, Vol. 5, pp. 219–226), that the anterior folds represent the original division between the head and thorax, is the one usually accepted. In rearity they are wholly thoracic in position, being nearer to the pro-mesothoracic line than to the head-thoracic boundary, and they are by no means vestigial structures, but specially developed organs of respiration.