STUDY OF CELL MECHANICS 457 



and during the periods of protoplasmic streaming. The de- 

 tailed history of the aster and of the chromosome during the 

 first monaster cycle had been worked out with such care by 

 Mrs. Boveri that little was left to be added to this side of the 

 problem. 



Series of eggs, in which the per cent of monasters was high, 

 were preserved at intervals of ten minutes or less, depending on 

 the stage. The preservatives used were Boveri's picro-acetic 

 mixture and sublimate acetic. After the usual treatment eggs 

 were sectioned at 7 microns and stained in iron haematoxylin 

 followed by light green. In practically all series whole mounts 

 were made of a few of the eggs stained in borax carmine. These 

 were very useful in orienting one as to the stages seen in 

 sections. 



One difficulty was encountered in the preserving fluids. 

 While the chromosomes and cytoplasm, in general, gave beauti- 

 ful preparations with both preservatives, the little protoplasmic 

 processes did not retain their shape well. This difficulty was 

 never fully overcome as these processes seemed extremely sen- 

 sitive to both mechanical and chemical stimuli. 



As was to be expected from the study of living eggs, a great 

 deal of variation was found in the appearance and behavior of 

 cell elements in the nine different series of eggs studied. The 

 typical behavior of the eggs will be described first and other 

 such variations as are illuminating will be taken up later. 



Since a monaster phase is a step in the formation of an amphi- 

 aster, it is very difficult to distinguish true monaster eggs until 

 the nuclear wall has disappeared and the aster has reached 

 considerable size. In the earliest stages the centrosphere of the 

 aster is small and deeply staining and the chromosomes are 

 bunched on one side. This stage is quickly followed by an 

 increase in the size of the centrosphere and a spreading of the 

 chromosomes over one side of the aster (figs. 16, 17). Once 

 reached, this condition persists a long time and corresponds, 

 as M. Boveri has pointed out, to the equatorial plate phase in 

 normal mitosis. 



A careful study of these monaster eggs points to two types 



