Chemotaxis of rabbit spermatozoa.

According to reviews (Tyler, 1955; Rothschild, 1956), chemotaxis of spermatozoa towards eggs has not been unequivocally demonstrated in animals. However, more recently, Suzuki (i96ia-c) has claimed that, in several species of Japanese bitterlings, the spermatozoa are attracted to a substance found in the egg micropyle. Suzuki's experiments, as well as earlier ones that aimed to prove or disprove the existence of sperm chemotaxis, were done on animals in which fertilization is external. So far as I am aware, no experiments on sperm chemotaxis in mammals have been published. In the absence of evidence for chemotaxis, it is assumed that collisions of spermatozoa with eggs, which, in most mammals, take place in the oviduct, occur solely by chance. The factors involved in such collisions are the concentration and movements of spermatozoa and, to a lesser degree, the slight movements of the egg induced by ciliary action and muscular contractions of the oviduct. Apparently the mechanism which brings the gametes together is highly efficient, since normally more than 90 % of the eggs are fertilized. The experiments described below were designed to find out whether sperm chemotaxis, in addition to chance meeting, plays a part in sperm-egg collision.