| Abstract: | The control of circadian activity rhythms (diurnal rhythms) in insects has been suggested to result by periodic neuroendocrine secretions. More specifically, Harker ('56) claimed that the locomotor rhythm in the cockroach, Periplaneta americana, is timed by a secretory “clock” located in the subesophageal ganglion. Later experiments by Harker indicated that this “clock” function failed unless the retrocerebral organs were left intact; allatectomy was said (no evidence given) to abolish a rhythm. The procedure for demonstrating a “clock” function in the ganglion involved transplanting it from a rhythmic donor into the hemocoel of an arrhythmic host and observing that the host subsequently became rhythmic. This result (without explicit information about the phase of the rhythm) does not warrant the conclusion that the ganglion acts as a clock. Therefore, I have attempted to confirm and extend these important results. Employing techniques essentially identical to Harker's, and using the same species of roach, I have been unable to find any evidence to support the original claim: (1) in 20 test animals, implantation of ganglia from rhythmic donors failed to re-instate a rhythm, and (2) allatectomy (22 cases) or removal of the entire retrocerebral complex (20 cases) did not interfere with the rhythm. The results of another series of experiments show that the cockroach brain is involved in the control of the activity rhythm. When the brain is surgically bisected (mid-sagittal) through the pars intercerebralis, arrhythmic activity patterns are immediately evoked. These continue for many weeks, but in a few cases rhythms ultimately “regenerate”. |
