Homolateral Synchronism of Lymphatic Hearts

Abstract

It is a long recognized fact that the opposite members of each of the 2 pairs∗ of anuran lymph hearts do not beat in unison. There has apparently resulted a universal assumption that the same lack of unison exists between the anterior and posterior members of these pairs; that the several automatic spinal centers, which are known to deliver groups of nerve impulses rhythmically to the lymph hearts, operate each independently of the others 1 (Fig. 1, a).

Such independence, however, is discovered to be purely contralateral. A simultaneous mechanical record of the beats of anterior and posterior hearts of the same side reveals a strict correspondence of rhythm, in contrast to the obvious lack of synchrony registered at the same time by a heart of the opposite side (Fig. 2). The synchrony is remarkably stable, persisting even in extreme arrhythmia (Fig. 3). Spinal section between 4th and 5th vertebrae abolishes the unison but not the activity of the homolateral organs, while curarization or stimulation of one fails to influence the other. The synchronizing influence is therefore of central and not of peripheral (proprioceptive) origin.

Evidence indicates that the regions of motor outflow to the lymph hearts of the same side, in both larval and adult forms, are connected (Fig. 1, b) through an intraspinal pacemaker system effecting an exclusively homolateral coordination.