CRITICAL THERMAL INCREMENTS FOR RHYTHMIC RESPIRATORY MOVEMENTS OF INSECTS

The rhythm of abdominal respiratory movements in various insects, aquatic and terrestrial, is shown to possess critical increments 11,500± or 16,500± calories (Libellula, Dixippus, Anax). These are characteristic of processes involved in respiration, and definitely differ from the increment 12,200 calories which is found in a number of instances of (non-respiratory) rhythmic neuromuscular activities of insects and other arthropods. With grasshoppers (Melanoplus), normal or freshly decapitated, the critical increment is 7,900, again a value encountered in connection with some phenomena of gaseous exchange and agreeing well with the value obtained for CO(2) output in Melanoplus. It is shown that by decapitation the temperature characteristic for abdominal rhythm, in Melanoplus, is changed to 16,500, then to 11,300—depending upon the time since decapitation; intermediate values do not appear. The frequency of the respiratory movements seems to be controlled by a metabolically distinct group of neurones. The bearing of these results upon the theory of functional analysis by means of temperature characteristics is discussed, and it is pointed out that a definite standpoint becomes available from which to attempt the specific control of vital processes.