Öz The secretory glands of insects, the corpora allata and corpora cardiaca found in the posterior part of the head have been studied by several authors. Although many investigations have been made, the role of the corpora cardiaca in the life of the organism has been very littie studied. It was found by physiolog^ical studies that the corpora allata produced a hormone which delayed metamorphosis and brought about retention of larval characters. The hormone which is produced by this gland is called “Juvenile Hormone,,. W i g gl es wo r t h, observed the marked inerease in secretory activity of the cells at the critical period and conciuded that this gland produced a hormone in Rhodnius prolixus (Hemiptera). This theory was backed exp3rimentally bytheauthor, İn 1936. At about the same time (1936) B ou n h i ol also found by experimental means that the corpora allata delayed methamorpho- sis in BoTnbix mori (Lepidoptera). P i e p h o (1940) performed similar experiments on Galleria and obtained the same results.