80 HELEN DEAN KING. 



same series are normal cannot be questioned. They show phe- 

 nomena exactly similar to those seen in eggs that have been 

 developing in water for some three hours, and leave no doubt but 

 that the earlier processes described above are normal in spite of 

 the unusual conditions to which many of the eggs were subjected" 



Four V-shaped chromosomes in which all traces of the polar 

 arms have disappeared are shown in Fig. 9. The arms of the 

 V's are broad flat plates which form a sharp acute angle with 

 each other. There is, in this case, no sign of a splitting in any 

 of the chromosomes which are all of the same size and shape 

 and arranged at the equatorial plate with the angle of the V 

 turned in towards the center of the spindle, a characteristic ar- 

 rangement of the chromosomes at this period. An equatorial 

 section of a spindle in the same stage as Fig. 9, is seen in Fig. 

 10, where all twelve chromosomes are present. In this egg 

 there are also found near the spindle a number of nucleoli which 

 are in the process of disintegration. 



Usually the first indication of any division of the chromosomes 

 is seen at the stage of Fig. 1 1 when the polar arms have entirely 

 disappeared and the chromosomes are broad V-shaped structures. 

 At this time the ends of the V's often show a deep indentation 

 (Fig. i i) indicating the longitudinal splitting of the chromosomes- 

 Occasionally I have found the first division coming in at an 

 earlier period before the entire disappearance of the polar arms. 

 Such a division is seen in the chromosome at the left in Fig. 7. 

 In all such cases the splitting is confined entirely to the lateral 

 wings and never extends into the polar arms. 



In the egg from which Fig. 12 was drawn, there are twenty- 

 four V-shaped chromosomes which are similar to the twelve 

 chromosomes in Fig. 10 in every respect except that they are 

 much narrower. They have been produced, I believe, by a 

 longitudinal division of the broad V-shaped chromosomes found 

 at an earlier period. In some of the chromosomes shown in 

 Fig. 12, the division for the second polar mitosis is seen. This 

 second division of the chromosomes is not visible, at this stage, 

 except in equatorial sections of the spindle. In longitudinal sec- 

 tions of the spindle the chromosomes always appear to be ar- 

 ranged in tetrad groups, one of which may be seen in Fig. 12. 

 Such a group is, in reality, a pair of V-shaped chromosomes with 



