The specific guidance mechanisms occurring in response to chemical
substances (often via Ca2+ controlled asymmetry of beating) or using guides developed
in various species because of special structures or tissues as well as by eggs in the
vicinity of a unique entrance point on egg surface, the micropyle present in some
species, are explored in this chapter. In order to avoid an excess of overlap with other
chapters, several situations are described either, in the case of "simple spermatozoa" in
species with external fertilisation. Part of this review chapter presents a tentative
synthesis of the distribution of chemotaxis during the course of evolution.
Keywords: Allomycetes, Brown algeas, Batracian, Calcium, Chemical gradient,
Cnidarian, Corals, Evolution, Echinoderms, Flagella, Fish, Ferns, Hydromedusa,
Insects, Jelly-fish, Mollusks, Salps, Siphonophores, Urochordates.
