Not separate brains, of course, but extensions (arrows in image above) of the main mass of their cerebral tissue. The reasons are explained at the Smithsonian's Newsdesk:
Smithsonian researchers report that the brains of tiny spiders are so large that they fill their body cavities and overflow into their legs. As part of ongoing research to understand how miniaturization affects brain size and behavior, researchers measured the central nervous systems of nine species of spiders, from rainforest giants to spiders smaller than the head of a pin. As the spiders get smaller, their brains get proportionally bigger, filling up more and more of their body cavities...Further discussion at the Smithsonian and in the original publication (Arthropod Structure and Development 521-529, doi10.1016/j.asd.2011.07.002).
Brain cells can only be so small because most cells have a nucleus that contains all of the spider’s genes, and that takes up space. The diameter of the nerve fibers or axons also cannot be made smaller because if they are too thin, the flow of ions that carry nerve signals is disrupted, and the signals are not transferred properly. One option is to devote more space to the nervous system...
Photo: Wcislo lab.
Surely you can't call any nervous tissue "brains"! Humans have nerve tissue running down the length of our spine and branching in to our legs so since we're drawing parallels here "Humans have brains in their legs!!"
ReplyDeleteBesides, insects and spiders don't have a centralized brain but rather a branching stem with several central nerve bundles. As such, the world "brains" is hardly applicable to any nervous tissue in these critters. Semantics, I know. But in this case the interesting bit about this publication is the relative increase in nervous tissue size with decreasing body size, not that the "brains are in their legs".
And let us not forget that a spider's penis is on it's leg...
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