The Imaginal Ecdysis of Blowflies. The Control of Cuticuar Hardening and Darkening

Abstract

1. Blood transfusion experiments show that normal hardening and darkening at the imaginal ecdysis of CaUiphora erythrocephala (Meigen) is brought about by the release into the blood of an active factor. Introduction of this factor into a newly emerged fly some 35 min. prior to the time at which it would normally be released is sufficient to prevent expansion. 2. The factor is normally released some 45 min. before the appearance of the first signs of darkening and between 3 and 15 min. after the fly has reached conditions suitable for expansion, that is at about the time of initiation of air-pumping. 3. Decapitation at emergence will prevent the initiation of normal hardening and darkening but not of secondary darkening. Evidently the head is concerned in the release or the control of the release of the blood-borne darkening factor. 4. The critical period for the prevention of normal hardening and darkening by decapitation lies between 3 and 15 min. after the fly has reached conditions suitable for expansion. 5. Isolated abdomina behave in a manner similar to decapitated flies but their reactions are complicated by secondary darkening associated with damage. 6. Flies deprived of their abdomina will expand at least partially but the rate of their hardening and darkening is reduced. 7. Damage reactions resembling secondary darkening in digging flies are more extensive after damage to internal organs such as the gut than to superficial organs such as the body wall. 8. Allowing for the effects of secondary darkening it is possible to demonstrate the occurrence of the blood-borne darkening factor by means of ligatures placed at emergence between the thorax and the abdomen. Under these conditions only the head and thorax exhibit normal darkening.