M. C. CHANG 111 



compound microscope a spermatozoon on the top of the zona 

 pellucida can be taken as being in the vitellus and that the pres- 

 ence of a nucleus in the ooplasm may not be a true male pronu- 

 cleus. Venge (1953) reported his fertilization of rabbit eggs in 

 a glass tube under partially anaerobic conditions. Although two 

 litters of young were produced when the treated eggs were trans- 

 ferred into recipient rabbits, he concluded that the development 

 was due to chance and not to controlled processes. Very recently, 

 Shettles ( 1955 ) reported the development of a human egg into a 

 morula after the treatment of an ovarian egg with sperm and 

 tubal mucosa in vitro. He neither excluded the possibility of arti- 

 ficial activation of the egg in his procedme nor mentioned the 

 probability of parthenogenetic cleavage in his paper. 



Moricard (1950) reported the penetration of a spermatozoon 

 into the ooplasm of 5 out of 21 rabbit eggs (24% ) in vitro under 

 relatively anaerobic conditions obtained by enclosing the eggs in 

 a piece of Fallopian tube placed under petroleum jelly. He stated 

 that the second polar body was not formed and that segmenta- 

 tion was not observed during 7/2 hours culture. Since the for- 

 mation of the second polar body occurs very soon after the 

 penetration of the spermatozoon into the viteUus, and since the 

 transformation of the sperm head into the male pronucleus is 

 also very fast (Pincus and Enzmann, 1932; Chang, 1951a), it is 

 rather peculiar that Moricard's photomicrograph (1950) shows 

 an intact sperm head and no second polar body after 7% hours 

 in culture. Later Moricard (1954) stated that about 30% of 

 rabbit tubal eggs are fertilizable in the utero-tubal secretion con- 

 taining spermatozoa. Since 24% of the eggs can be penetrated 

 in vitro under anaerobic conditions by sperm obtained from the 

 vagina (?), it is not clear whether the 30% of fertilized eggs were 

 due to anaerobic conditions or due to the employment of uterine 

 sperm. 



After the demonstration that ejaculated sperm require a cer- 

 tain length of time in the female tract to develop their fertilizing 

 capacity (Chang, 1951b; Austin, 1951c), Dauzier et al. (1954) 

 reported that fertilization of rabbit eggs in vitro can be achieved 

 by using sperm recovered from the genital tract of rabbits 12 



