262 A. RICHARDS. 



established axis. Whether this is by an actual revolution of the 

 entire vesicle, or only by a change of shape so that its short 

 diameter now becomes its long axis is not clear, but it seems 

 probable that the former process takes place. When condensa- 

 tion occurs and the new prophase chromosomes are formed they 

 show the polarity in a very striking manner, almost every chromo- 

 some in the spireme stage being oriented in the long axis of the 

 forming spindle (see Fig. 22). This of course is to be expected 

 in view of the definite polarity of the vesicles in the prophase as 

 shown in Fig. 17. 



In reconstructing nuclei where the fixation is not quite perfect, 

 the walls of the vesicles sometimes cannot be seen. They are 

 very delicate and require a very complete fixation if they are to 

 be preserved in their entirety. When the nucleus enters upon 

 the first steps of the prophase and liquid is extruded from the 

 vesicles so that they shrink or condense, the walls are particularly 

 difficult to preserve. This results in an artificial running to- 

 gether of the granules into irregular clumps. Yet the area form- 

 erly occupied by the vesicle is still to be seen separating one 

 clump of chromatin from the next, and the nuclear membrane is 

 still retained although in a shrunken condition. The chromatin 

 so massed by the irregular plasmolysis of the walls of the vesicles 

 in some instances comes to resemble a prophase chromosome. 

 Mere clumps of chromatin granules, however, with nuclear 

 membrane intact and the inner vesicle walls gone indicate 

 artifacts rather than normal conditions. Yet even they serve 

 to suggest certain facts which are represented in the normal nuclei. 



The new chromosomes arise within the old vesicles. When 

 the waiter first began the study of this phase of the subject, he 

 was led to expect that the shrinkage which takes place at the 

 beginning of the prophase as shown in Figs. 13, 17, and 1 8, 

 would continue and the formation of the new chromosomes 

 would be simply the reverse of the process by which the vesicles 

 had been formed. Such is not the case, however, for it is now 

 certain that the new chromosomes arise endogenously. The 

 formation begins within the vesicle with the gradual increase in 

 size and the aggregation of the chromatin granules upon its walls. 

 The typical condition of the vesicles during rest shows small 



