1. In the tobacco hornworm, wing spreading involves a stereotyped series of movements which take 74 min to complete and which include two components, wing folding and wing inflation.
2. Moths decapitated at the moment of eclosion show neither wing inflation nor wing folding. If decapitation is delayed until 5 sec after emergence, then the full wing-spreading behaviour is displayed.
3. Newly emerged moths which are confined show intense digging-behaviour and delay the onset of wing spreading until after their release. Decapitated moths attempt to spread their wings immediately, regardless of whether or not they are confined.
4. Surgical experiments showed that the brain was not required in a neural capacity in order for wing spreading to occur; it was needed only as a source of the eclosion hormone. The neural influence of the suboesophageal ganglion was required until immediately after eclosion.
5. Newly emerged moths whose abdomens had been removed showed wing-folding behaviour. No inflation occurred and the duration of wing folding was much longer than normal. It was concluded that wing-folding behaviour was centrally programmed but that the abdomen could modify the length of the programme.
6. Injections of bursicon into abdomenless moths reduced the duration of wing-folding behaviour to almost normal levels. Therefore, in some manner, bursicon has an important role in determining when wing-folding behaviour will come to an end.