330 KING. [Vol. XVII. 



6. The line of radiation shortens gradually and a number of small gran- 



ules appear in the midst of the rays. These granules soon fuse 

 into irregular clumps staining like chromatin. 



7. The debris from the germinal vesicle is carried to the black pole and 



forms the cicatricula. 



8. At the beginning of nuclear disintegration the chromosomes become 



arranged in twelve pairs. The ends of each pair fuse, forming a 

 closed ring near which a small aster suddenly appears. 



9. The first polar spindle is formed at some distance below the surface of 



the ^^%, probably from the line of radiation. The large polar astro- 

 spheres have no centrioles. 



10. The asters accompanying the rings have disappeared when the chromo- 



somes are arranged on the spindle. The twelve chromatin rings 

 split longitudinally, forming twenty-four closed rings which later 

 divide at the points of union of the two original chromosomes, form- 

 ing forty-eight half rings. 



11. On its way to the peripherj-, the spindle loses its astrospheres. The 



chromatin material becomes greatly concentrated, halves of sister 

 chromosomes apparently re-fuse, and the spindle seems to have but 

 twenty-four dumb-bell-shaped chromosomes. 



12. The first polar division separates the two chromosomes which originally 



fused to form a chromatin ring. 



13. The second polar spindle has no astrospheres and is smaller and more 



slender than the first polar spindle. In the second polar division 

 sister-chromosomes separate and there is an equal division in Weis- 

 mann's sense. Twelve chromosomes, one-half the normal number, 

 are left in the ^g% after the second polar body is given off. 



14. There is no evidence that a centrosome is contained in any part of the 



spermatozoon of Bufo lentiginosus. 



15. The spermatozoon can penetrate any point of the upper hemisphere. 



An astrosphere is formed at its anterior end before the middle-piece 

 has entered the &gg. The entire spermatozoon enters the egg, the 

 tail and middle-piece soon disappearing. 



16. The male and female pronuclei are apparently alike in structure ; but 



they can be distinguished until nearly the time of fusion, as the 

 former is always accompanied by the astrosphere ; the latter lies in 

 close contact with the egg substance and has no sign of a radiation 

 around it. 



17. The astrosphere is at first round and uniformly granular. It soon 



becomes oblong, many rays appear around it, and it then divides 

 into two separate astrospheres. 



18. The two pronuclei fuse in the upper hemisphere. The segmentation 



nucleus lies between the two astrospheres, which appear as rounded 

 structures composed of an irregular meshwork, the rays having 

 entirely disappeared. 



