Abstract
1. 1. The heart and associated tissues of spiders that had been stung by a mud-dauber wasp were examined for responses to the toxin. Microelectrode recordings of myocardial cell membrane depolarizations were obtained from spontaneously beating hearts in situ. Transmission electron microscopic examination was made of the cardiac ganglion, myocardium and hemocytes. 2. 2. The myocardial cell depolarizations in paralyzed and unparalyzed spiders were 20–40 mV in amplitude and 300–500 msec in duration. The depolarizations did not display an overshoot, and individual excitatory synaptic potentials were seen in the responses. Therefore, the normal electrical events in the heartbeat, which is neurogenic, were not interrupted by the toxin. 3. 3. No alteration in the ultrastructure of the cardiac ganglion, neuromuscular synapses, myocardial cells or hemocytes was apparent in the material obtained from paralyzed spiders.
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