CHROMATIN DEVELOPMENT AND HEREDITY 245 



56 are anaphase spindles from the former cross. Although di- 

 vision became very irregular in this experiment and a spindle 

 with the full quota of chromosomes is rare, nevertheless two 

 types of chromosomes characteristic of Ctenolabrus, rods and 

 hooks, appear. None of the typical long Fundulus chromosomes 

 are present in figure 56 and only one appears in figure 55. Some 

 of the short rods shown may have originated from the sperma- 

 tozoon, but the hook-shaped elements are undeniably chromo- 

 somes belonging to the egg. 



The cleavage rhythm of the developing eggs of Stenotomus and 

 Ctenolabrus is approximatey the same. The hybrid eggs of the 

 cross Ctenolabrus 9 X Stenotomus cf resemble the pure Cteno- 

 labrus eggs in the rate of the early cleavages. 



No abnormalities in the behavior of the chromosomes during 

 the early cleavages have been found. Figures 46 to 54 show in 

 sequence the important stages studied. The union of the male 

 and female pronuclei is shown in figure 46. Figure 47 is of a 

 stage just after the disappearance of nuclear walls and before 

 the chromosomes have entered the spindle. In figure 48 a 

 slight advance is shown. The chromosomes lie on the spindle 

 between the asters, but are not yet drawn mto the equatorial 

 plate. In both of these figures two rather well-defined groups 

 of chromosomes appear. In the formation of the equatorial 

 plate this grouping is lost and is no longer evident in the ensuing 

 anaphases, as may be noted in figures 50 and 51. These figures 

 show, also, the form of the elements of the hybrid complex and 

 the absence of any interference in their division. Figure 49, 

 of a polyspermic egg, is given because it shows very well the 

 early separation of the chromosomes, a stage not observed in the 

 monospermic eggs. The unimpeded splitting of the chromosomes 

 is clearly demonstrated. Postanaphase stages of the second 

 cleavage likewise reveal nothing abnormal in the nuclear behavior. 



Figure 52 is a drawing of the fourth cleavage stage in which 

 pairs of chromosomes can be identified. Not all of the chro- 

 mosomes could be included in the drawing. 



The occurrence of nmnerous vacuoles in the cytoplasm of the 

 eggs of this lot is the only abnormality noted, but whether this 



