CHEOMATIN— DEVELOPMENT AND HEREDITY 247 



original contribution of the egg and sperm is the fact that during 

 the early metaphase two groups of chromosomes can be dis- 

 tinguished on the spindle. Very often one of the groups is 

 massed together in such a way that single chromosomes cannot 

 be recognized, while in the other group the elements are well 

 separated. Figure 58 shows the characteristic arrangement of 

 the two clusters of one spindle. This may be considered rather 

 important as an indication of physiological differences which 

 are the cause of subsequent abnormalities. 



A large number of dividing cells of the first three cleavages 

 were studied. These differ strikingly from those of the recipro- 

 cal cross. All show lagging chromatin, some to a very marked 

 degree. Figures 59 to 62 present four first-cleavage anaphases. 



Figure 59 includes three sections arranged m the order that 

 they appeared on the slide. Many of the chromosomes on the 

 spmdle are dividing normally. The plane of the sections prob- 

 ably corresponds with that of the section in figure 58. In 

 figure 61 undivided chromosomes are passing to the poles. 

 This forms indisputable evidence of the unequal distribution in 

 this hybrid of chromosomes durmg cleavage. It is only in 

 anaphase stages that such an abnormal occurrence could be 

 detected. 



Figures 67 and 68 are of anaphases of the second cleavage and 

 figures 70 and 71 illustrate the same stages from the thhd cleav- 

 age. These figures, as well as many others in the material, 

 show a condition which suggests that some of the chromosomes 

 have undergone a process of fragmentation. Small round 

 bodies, which behave like chromosomes, appear frequently in 

 these stages. They have been observed only occasionally in 

 the normal Ctenolabrus eggs and m the reverse cross between 

 Ctenolabrus 9 and Stenotomus cT. However, the conditions 

 here, where all of the chromosomes are scattered over the spindle, 

 are more favorable for a study of the true form of the chromo- 

 somes than in normal mitoses, where the chromosomes moved in 

 close ranks to the poles, and it may be that these small elements 

 are of normal occurrence, but have hitherto escaped notice. 

 I am inclined to favor the idea of their fragmentary nature. 



