264 A. RICHARDS. 



formed filial chromosomes while at the same time the walls of 

 the old vesicles have not yet disappeared. In the upper part 

 of this figure they are less distinct, but elsewhere the vesicles are 

 easily seen in their entirety. The walls stand out clearly and 

 take the orange stain strongly, so that there can be no mistake 

 about their presence. The spheres are not shown in the plane 

 of this section, but the spindle fibers indicate the polarity with 

 most of the chromosomes oriented in the spindle axis. 



Of the greatest importance is the evidence presented in Fig. 22. 

 The presence in the vesicles, the walls of which are still intact, 

 of the new filial chromosomes, for these spireme structures are 

 now definite chromosomes, is the crux of the argument for 

 chromosomal continuity. It is not difficult to follow through 

 the history of the vesicles from the time of their earliest forma- 

 tion out of the metaphase chromosomes thorugh anaphases, 

 telophases, and interkinesis, and to see that the vesicle represents, 

 so far as the chromosomal bodies are concerned, a continuous 

 unit of structure. The parental chromosomes are not lost in 

 the vesicle stage; they are merely metamorphosed, appearing 







in a new form and the chain of the continuity is never broken. 

 In the vesicles the continuity is still maintained throughout the 

 resting period of the nucleus and it is only in the late prophase 

 of the daughter generation that the vesicular walls disappear. 

 But before that disappearance, the new filial chromosomes have 

 been formed and are in the so-called spireme stage, representing 

 uninterruptedly the persistent continuity of the units with 

 which the cycle started in the parental metaphase. In this 

 spireme stage the chromosomes are as definitely chromosomes 

 as in the metaphase which immediately succeeds, and they have 

 only to condense further and to attach themselves to the spindle 

 to enter the metaphase, a process obviously favored by the dis- 

 solution of the nuclear walls. 



In Fig. 23 all traces of the vesicle walls have disappeared and 

 the chromosomes resemble the late prophase chromosomes of 

 many animals. This is the only case in which the longitudinal 

 split is seen, and it may be that it is really precocious, or that 

 the figure represents the facts only in part. In most nuclei in 

 which the chromosomes are well formed the spindle development 



