The heartbeat of the spider, geolycosa missouriensis

1. 1. Heart rate in Geolycosa missouriensis is described. Resting unrestrained spiders have a mean heart rate of 48 beats/min but immediately after forced exercise, rates as high as 176 beats/min are recorded. Restrained resting spiders have a mean rate of 138 beats/min. 2. 2. An isolated heart preparation is described. In isolated hearts the mean rate of beating is 62 beats/min. 3. 3. Electrical activity recorded from isolated hearts is of the oscillatory type characteristic of neurogenic hearts. 4. 4. The cardiac nerve on the dorsal surface of the heart is shown to contain approximately fifty nerve cell bodies and thus this nerve appears to be a cardiac ganglion.