| Abstract: | (1) Premature reversal of direction of heart-beat in Bombyx was induced in spinning larvae and those about to spin by blocking the 3 most posterior pairs of spiracles with Brunswick black, in accordance with the experiments of Yokoyama. (2) This method and the injection of lactic and other acids paralyze the muscles of the body wall and heart in that region, thus preventing forward and permitting backward beating. (3) Attempts to produce periodic reversal in the larva in the early days of the 5th stage by Yokoyama's methods failed. (4) The application of ether, alcohol, or xylol to the 3 posterior pairs of spiracles, or immersion of these segments in alcohol, was effective in inducing premature reversal at the close of the 5th stage, exclusively forward beating being resumed as soon as narcosis disappeared. (5) Amputation of the posterior end of the body of the larva, including the end of the dorsal vessel in abdominal segments 7 and 8, did not prevent forward peristalsis. (6) Amputation of head and thorax from the abdomen of a pupa did not interfere with normal periodic reversal in the abdomen. (7) Thus periodic reversal in the dorsal vessel takes place without the intervention of any terminal ganglia. (8) The suggestion of Yokoyama and earlier writers (Bataillon, Fischer) that general acidosis initiates normal backward beating is not corroborated. (9) The metabolic gradient of the larval dorsal vessel is never lost, but intermittently neutralized in the prepupa, pupa and adult by increased metabolic action at two other points: the central node (in the young pupa) and the aorta with its mesothoracic pulsating vesicle (in the adult). (10) These gradients are adaptations to the large influx of hemolymph into the dorsal vessel at three principal regions. |
