226 \V. M. SMALLWOOD. 



such of it as appears in the section, is near one end of the female 

 pro-nucleus and much smaller. In Fig. 23 is shown another 

 form of the prophase. This drawing was taken from the be- 

 ginning of the second cleavage. The small prophase spindle 

 lies entirely within the centrosphere and the chromosomes are in 

 the form of vesicles. That these vesicles are modified chromo- 

 somes is proved by the condition of the chromosomes at the 

 opposite pole of the old spindle where the process was not as 

 advanced. Here some of the interzonal fibers were still in con- 

 tact with the partly transformed chromosomes. The successive 

 cleavage is so rapid in this instance that the new spindle has 

 formed before the vesicles have united into a single vesicle, the 

 nucleus. Nevertheless a normal spindle will result when the 

 chromosome vesicles are transformed again into chromosomes. 

 It is the study of such changes as these in the chromatin that 

 convinced me that the vesicles in Fig. 10 were modified chromo- 

 somes and the vesicles in Figs. 1216 were formed through the 

 influence of chromatin astray in the cytoplasm. A third form of 

 the prophase is quite common, Fig. 24, PI. IV., where the nu- 

 cleus is much elongated or somewhat irregular in outline. This 

 prophase stage is farther advanced than the two previously de- 

 scribed. The asters are larger and the forming spindle fibers 

 more pronounced at each end. The chromatin has begun to take 

 a deeper stain. In some respects all of these three forms of 

 prophase are different, but the differences are not fundamental, and 

 plenty of similar variations are known in other animals. They 

 are all unmistakably by the mitotic process. 



The metaphase is as typical as exists in any mitotically divid- 

 ing cell. The chromosomes split and move to each pole, Figs. 

 23, 26, 27, PI. II. During the late anaphase and early telophase 

 the chromosomes become transformed into vesicles, Figs. 27, 23, 

 may or may not unite into a single vesiculate nucleus before the 

 next cleavage. I have been able to trace the nucleus contin- 

 uously from its state in the unmaturated egg through all of the 

 cleavage states. At no times does it dissolve other than in the 

 normal mitotic changes. At no time does the total contents of 

 the nucleus become dissipated throughout the cytoplasm to reform 

 into separate nuclei. Other than the chromatin changes just 



