Sperm chemotaxis in mammals

The occurrence of sperm chemotaxis in mammals was established in vitro only at the last decade. As a matter of fact, until then there had been resistance to the concept of mammalian sperm chemotaxis for two main reasons. First, in mammals in which fertilization is internal and very large numbers of spermatozoa are ejaculated directly into the female reproductive tract (4 0X10 in humans [185] 10 -10 in mammals in general [66]), chemotaxis was believed to be unnecessary because a sufficient number of spermatozoa would reach the egg coincidentally. Second, technical difficulties in studying mammalian sperm chemotaxis prevented the acquisition of conclusive evidence. The primary technical difficulty was a very low signal-to-noise ratio in the measurements, resulting from the fact that only a small fraction of the sperm... 

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