444 ^-^^ AMERICAN NATURALIST. [Vol. XXXVIII. 



decrease in size, or, if large, it may fragment. Strasburger, in 

 1895, advanced the view that the spindle actually drew upon the 

 substance of the nucleolus for the material and energy necessary 

 to its development. The evidence in support of this suggestive 

 theory lies chiefly in the development of the spindle coincident 

 with the dissolution of the nucleolus. There is also some evi- 

 dence that the nucleolus contributes material to the developing 

 chromosomes. Small globules, which stain as the substance of 

 the nucleolus, may sometimes be found adhering to the chromo- 

 somes as though becoming incorporated in them. These sub- 

 jects are naturally very difficult of investigation because stain 

 reactions cannot be depended upon with certainty and are not, 

 of course, chemical tests. Then the behavior of the nucleolus 

 during mitosis is exceedingly variable, since it sometimes disap- 

 pears quickly and sometimes remains intact, and it becomes a 

 very difficult matter to determine its importance. The nucleolus 

 is probably not absolutely necessary at any stage in mitosis, for 

 both spindle fibers and chromosomes develop apart from this 

 structure ; but it does seem to be established that the substance 

 of the nucleolus is generally drawn upon by the cell, especially 

 during prophase, when numerous spindle fibers are organized and 

 the amount of chromatin is being largely increased. Experi- 

 ments of Hottes, which unfortunately have never been published, 

 have an important bearing on these problems. 



If the nucleoli are not entirely dissolved they are frequently 

 thrpwn out of the spindle into the cytoplasm, where they may 

 lie for long periods as deeply staining globules which are some- 

 times called extra nuclear nucleoli. It is probable that very many 

 of the bodies that pass under this cumbersome title have no 

 relation whatever to the nucleolus. The cytoplasm frequently 

 contains globules that may be coagulated or precipitated food 

 products, and all of these stain similarly to nucleoli. 



Metaphase. — The period of mitosis termed metaphase is, to 

 speak precisely, the time when the two halves of the split chromo- 

 some separate from one another. However, this is a period of 

 such short duration that for practical purposes nuclei are consid- 

 ered in metaphase when their chromosomes are' lined up at the 

 nuclear plate. The metaphase of mitosis is generally the most 



