Number of neurons in the nervous system
|1,000,000,000,000||Homo sapiens (maybe 1014)|
|50,000,000||Stickleback (small fish)|
|20,000||Sea slug (Aplysia)|
|381||Thread worm male|
|302||Thread worm (hermaphrodite)|
*NB* for numbers over 20,000 these numbers are usually speculative estimates. The figure of 1012 or 1 billion for the human brain is an old one, but it serves for a rough comparison with the chimpanzee and rhesus monkey. |
In general, number of neurons is correlated with brain weight or volume, but not exactly, as larger animals have larger neurons.
An internet site listing some brain weights is at http://faculty.washington.edu/chudler/facts.html.