ORDERS OF INSECTS WITH HEART-BEAT REVERSAL

Abstract

Representatives of four orders of holometabolous insects, Diptera, Coleoptera, Lepidoptera, and Hymenoptera have shown periodic (intermittent) heart-beat reversal in the pupa and imago. In an adult crane fly, the number of forward beats per phase exceeded the backward, but the average rates of beating in each direction were almost equal. Gradual retardation of rate occurred within each single forward phase, slight acceleration within each backward phase. In the adult beetle there was likewise no marked difference between the average rates backward and forward. A very gradual retardation in rate was observed during each phase whether backward or forward. Central beating in both directions from the pulsating vessel of the metathorax or from the middle of the abdomen occurred. A few converging waves conflicting at the third abdominal segment were observed. Saline solution quickened the rate. There was an occasional tendency to beat in groups of two without change of rate. Pauses sometimes broke up a long phase, each being of about the same length as the groups among which they were interpolated. In Hymenoptera, long backward and forward phases, each a half hour or more in length, were characteristic of Sphex and Opheltes. The rates were rapid. In Sphex the rate backward was gradually retarded; in Opheltes the rate during any long phase was nearly constant, though during one backward phase of 47 minutes there was slight acceleration.In general, normal reversal occurs independently of the central nervous system and is essentially myogenic. Stimuli from the head, wings, legs, and genitalia, however, secondarily affect peristalsis in detail, producing variations in rate, length of phase, number of beats in a phase, and occasionally probably reversal. Central beating does not depend upon special ganglia but upon local regions of higher irritability (or greater local inflow of haemolymph from the pericardium), which vary somewhat even in the same individual.