2CJO A. RICHARDS 



EXPLANATION OF PLATE IV. 



FIGS. 26 to 29 are from a grastrulation stage of F 9 X Ccf; sperm radiated 

 fifteen minutes before fertilization, by which the sperm chromatin was killed so 

 that it took no further part in development. 



FIG. 26 shows the central spindle forming across one side of the nucleus. 



FIG. 27 is a later stage showing the central spindle half dividing the nucleus. 

 Not female and male parts, for the sperm's contribution of chromatin was killed 

 as shown in Fig. 29, an anaphase in which all chromosomes are of the Fundulus 

 type, and in Fig. 30, which is a cross-section of such a nucleus showing the groove 

 through which the central spindle passes. 



