122 THE MAMMALIAN EGG 



12 hr previously, and a small volume of this suspension was added 

 to the eggs. The glass tubes were sealed at both ends with liquid 

 paraffin. The preparation was incubated for 2 to 6 hr and the eggs 

 then fixed and prepared for histological examination. Some eggs 

 were transferred to homologous serum and kept in culture (in glass 

 tubes) to permit cleavage before being removed for histological 

 study. In sections of eggs, various stages were seen in the develop- 

 ment of two nuclei, which resembled in general appearance and 

 staining reactions normal male and female pronuclei. Sperm tails 

 could sometimes be identified in the vitellus and, in some of the 

 experiments, some of the eggs contained supplementary spermatozoa 

 in the perivitelline space. With the longer periods of incubation, 

 some eggs underwent cleavage and this appeared to have occurred 

 in a normal manner. Very few eggs that were subjected to the same 

 treatments, but without the addition of spermatozoa, showed any 

 sign of activation. 



Moricard's work was of a somewhat similar nature: he placed the 

 freshly recovered rabbit eggs in a watch-glass under liquid paraffin 

 and added to them a suspension of spermatozoa recovered from the 

 uterus of an animal that had been mated 10 hr previously. After 

 incubating the eggs, he found that spermatozoa could be seen in 

 the perivitelline space of whole unfixed eggs (examined by phase- 

 contrast microscopy) and noted the development of pronuclei. 



In addition to the cytological data, Dauzier and his associates 

 reported that they obtained only negative results when suspensions 

 of freshly ejaculated spermatozoa were used. No penetration was 

 recorded when the female rabbit, from whose genital tract the 

 sperm suspension was prepared, had been mated only 4 or 6 hr 

 previously, and the frequency increased with longer intervals from 

 mating, from some penetration at 8 hr up to a maximum of about 

 25 per cent at 12 hr. At 16 hr, the penetration frequency was low 

 again. In the most recent report of the series, evidence is adduced 

 in support of the idea that rabbit eggs emit a form of 'fertilizin' 

 which tends to inhibit sperm penetration and which is normally 

 neutralized by a substance in the secretions of the female genital 

 tract (see p. 115). Consistently, eggs washed several times after 

 recovery were found to have been penetrated much more frequently 

 (about 70 per cent) and to contain more supplementary spermatozoa 

 than eggs seminated without this treatment. 



