PRELIMINARIES TO FERTILIZATION 

 IN MAMMALS 



C. R. AUSTIN AND M. W. H. BISHOP: 



NATIONAL INSTITUTE FOR MEDICAL RESEARCH, 

 MILL HILL, LONDON 



Since von Baer described the mammalian primary oocyte and 

 Barry observed spermatozoa within the rabbit egg, work on fer- 

 tihzation in mammals has been directed chiefly toward the eluci- 

 dation of cytological problems. In recent years, however, increas- 

 ingly more attention has been paid to the events occm'ring 

 between coitus and the arrival of the spermatozoon in the egg 

 cytoplasm. As a result, it is becoming evident that the prelimi- 

 naries to fertilization are of a highly complex nature and further 

 that, in large measure, they determine the successful union of 

 the gametes and the normal outcome of syngamy. 



Among many invertebrates and lower vertebrates the gametes 

 are released into the surrounding aqueous medium, which con- 

 stitutes their environment of fertilization. As the spermatozoa 

 approach the eggs they experience the influence of chemical 

 substances associated with the eggs, and on their part the sperma- 

 tozoa arouse reactions in the eggs during the course of penetra- 

 tion, so that interaction between egg and spermatozoon becomes 

 a feature of the environment of fertilization. 



With the occurrence of ovulation and ejaculation the mamma- 

 lian gametes are projected into their environment of fertilization, 

 which thus consists of the accessory secretions of the male and 

 the entire genital tract of the female. From the moment of their 

 release into the female' tract, the spermatozoa come under the 

 manifold influences of this environment, all of which may affect 

 the incidence or course of fertilization. A contribution is also 

 made by the egg to the environment of the spermatozoon, al- 



71 



