<P> In the wood mouse Apodemus sylvaticus, sperms aggregate in' trains' that are better able to fertilize eggs because they are more capable of navigating the viscous environment of the female reproductive tract . The trains move in a sinusoidal motion . </P> <P> Sperm motility is also affected by certain factors released by eggs . </P> <P> Sperm movement is activated by changes in intracellular ion concentration . The changes in ion concentration that provoke motility are different among species . In marine invertebrates and sea urchins, the rise in pH to about 7.2--7.6 activates ATPase which leads to a decrease in intracellular potassium, and thus induces membrane hyperpolarization . As a result, sperm movement is activated . The change in cell volume which alters intracellular ion concentration can also contribute to the activation of sperm motility . In some mammals, sperm motility is activated by increase in pH, calcium ion and cAMP, yet it is suppressed by low pH in the epididymis . </P> <P> The tail of the sperm - the flagellum - confers motility upon the sperm, and has three principal components: </P>

Where do sperm gain the ability to​ swim
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