No. 2.] THE EGG OF BUFO LENTIGINOSUS. 313 



fibers are well defined and extend unbroken from pole to pole, 

 where they converge sharply and run into two distinct as- 

 trospheres (PI. XXIX, Fig. 26). These astrospheres are 

 considerably larger than the asters which accompanied the 

 chromatin rings at an earlier period, and the rays are much 

 longer and thicker. Their structure, however, appears to be 

 similar to that of the asters in that the center of each astro- 

 sphere seems to be composed of only the ends of the rays 

 closely massed together, and all methods of fixation and stain- 

 ing fail to disclose the presence of a distinct central body. 



The asters accompanying the chromatin rings at the stage of 

 Fig. 24 have entirely disappeared by the time the spindle is 

 formed, and the rings are apparently being drawn towards the 

 spindle by some sort of an attractive force, the nature of which 

 cannot be determined. The chromatin rings that have reached 

 the spindle (Figs. 25, 26) are found to be much larger than 

 those some distance away (PI. XXIX, Fig. 27), and instead of 

 being composed of a single series of large microsomes, as in 

 the previous stage, they are now distinctly seen to consist of a 

 double series of smaller microsomes. TJie rijigs must, there- 

 fore, midej'go a longitudinal splitting at this stage. Each of 

 the sister rings has two knob-like thickenings, undoubtedly 

 representing the place of union of the two chromosomes that 

 fused to form the ring (Fig. 26). Chromatin rings with such 

 thickenings have been found by Flemming ('87) in the hetero- 

 typic type of division in the spermatocytes of the salamander 

 testes. After the double chromatin rings have arranged them- 

 selves on the spindle each breaks into four parts at its knob- 

 like thickenings (PI. XXIX, Fig. 28), and thus the chromosomes 

 which fused to form the rings are separated and split longi- 

 tudinally. 



During its migration towards the black pole, the spindle 

 shortens and becomes much more slender, — a phenomenon 

 seen by Korschelt ('95) during the migration towards the periph- 

 ery of the first polar spindle of Ophryotrocha, by Biitschli 

 ('76) in Cucullames, and by Erlanger ('95) in Macrobiotus mac- 

 ronyx. The astrospheres fade away and have completely dis- 

 appeared by the time the spindle has reached the periphery, so 



