Abstract
1. 1. Embryonic and adult hearts of the house cricket Acheta domesticus were studied in the electron microscope and with intracellular microelectrodes. 2. 2. Autorhythmic activity and synchronized heartbeat were observed in the embryo at 6 days postoviposition (dpo). 3. 3. Intercalated discs were not observed in the embryonic heart, nor were neural elements. 4. 4. Embryonic heart cells (6 dpo) averaged 3.5 μm in diameter, with a single nucleus, a single myofibril, closely apposed mitochondria and complete sarcomeres. 5. 5. Adult cricket heart cells averaged 6.8 μm in diameter with tortuous intercalated discs and numerous neurosecretory axons in which three types of intra-axonal granules were identified. 6. 6. Electrical potentials rise and fall smoothly with no overshoot. Discrete background activity appears to be postsynaptic in nature.
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