T]he octopus nervous system contains about 500 million nerve cells, more than four orders of magnitude greater than in other molluscs (garden snails, for example, have around 10,000 neurons) and more than two orders of magnitude more than in advanced insects (cockroach and bee, for example, have around a million neurons), which probably rank next to cephalopods in invertebrate behavioral complexity. The number of neurons in the octopus is well into the range of amphibians such as the frog (~16 million) and small mammals such as the mouse (~50 million) and rat (~100 million), and not much fewer
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