288 A. RICHARDS. 



EXPLANATION OF PLATE III. 



FIG. 19. Pure Fundulus material. First step toward chromosome formation 

 is shown in the condensation of chromatin granules on vesicle walls leaving the 

 centers of the vesicles relatively empty. 



FIG. 20. Pure Fundulus material. Further condensation and beginning of 

 new chromosome as a row of granules, chromomeres, extending out into the center 

 of the vesicle. Drawn as nearly as possible at one level. 



FIG. 21. All chromatin granules now formed into the new chromosome anlage. 

 But the vesicular area can yet be distinguished. Only one level drawn. 



FIG. 22. F9 X Fcf ; radiated three minutes after fertilization. Prophase of 

 third cleavage, showing distinctly old vesicular walls, and also new chromosomes 

 already formed within. Certain of the vesicles show walls especially clearly. 

 Only one level drawn. 



FIG. 23. From slide belonging to Miss Pinney. Third cleavage. The only 

 case observed showing the splitting of the chromosomes. The condition of spindle 

 and asters suggest that this splitting may be precocious. 



FIG. 24. F9 X Fcf ; radiated three minutes after fertilization. Sixth cleav- 

 age prophase, oblique section. Traces only of the old vesicular walls are left while 

 the astral rays are making their way into the chromosomes which are more con- 

 densed. 



FIG. 25. F9 XFcf; normal. Fourth cleavage, late prophase. As usual, 

 only part of chromosomes are shown. Spindle formation completed and chromo- 

 somes are condensing and forming the equatorial plate. 



