ORDERS OF INSECTS WITH HEART-BEAT REVERSAL

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Abstract
Representatives of 4 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 (Pachyrhina jerruginea) 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 (Prionus laticollis) 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 3rd abdominal segment were observed. Saline solution quickened the rate. There was an occasional tendency to beat in groups of 2 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 30 min. 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 hemolymph from the pericardium), which vary somewhat even in the same individual.

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