FERTILIZATION AFTER INITIATION OF DEVELOPMENT. 287 



any possible doubt that sperm do enter the blastomeres (Fig. 5) 

 but the normal effect of a spermatozoon entering an egg is not 

 apparent. Many of the sperm heads lie within the cytoplasm 

 entirely unchanged, while others are seen to have increased in 

 size from swelling, but most of these are undergoing evident 

 degeneration, of which various stages can be seen (Fig. 6). The 

 chromatin gradually loses its staining reaction, appearing much 

 clearer than the unchanged sperm heads outside of the eggs, 

 and some have so entirely lost their staining capacity that they 

 appear only as clear vacuoles scattered throughout the cyto- 

 plasm of the half-eggs. Out of the vast numbers of sperm 

 heads observed within these half-eggs only one was found that 

 contained an indication of a good sperm aster. A few of the 



FIG. 6. X 3,000. Part of section of a quarter egg showing presence of both 

 unchanged and degenerating sperm nuclei. No indication of fertilization changes. 

 Same exposure as Fig. 5. 



blastomeres are undergoing segmentation as a result of the 

 hypertonic treatment and the spindles appear quite normal. 



Here then the spermatozoon not only does not find a congenial 

 environment in which normal reactions can go on, but the sur- 

 roundings are even hostile and result in the disintegration of the 

 spermatozoon without its having undergone any changes that 

 indicate the least possibility of a fertilization reaction. 



4. Conclusions of Section IV. 



This cytological examination very clearly reveals the fact 

 that the unfertilizable condition of eggs subsequent to an ex- 

 posure to hypertonic sea-water is not due to the failure of a 

 spermatozoon to enter the egg but that it is due to a change 

 within the egg itself. Certain changes that are to be associated 



