Regarding nutrient and oxygen flow, would be interesting to compare the brains of a large bee like Xylocopa violacea (violet carpenter bee [1]) with that of a small bat like Craseonycteris thonglongyai (bumblebee bat [2]).
These two species are of about the same size (3-5 cm), yet one is an insect and the other is a mammal. Actually, the bee is larger than the bat! I wonder which one has more neurons.