520 Wisco7isin Academy of Sciences,, Arts_, and Letters. 



EXPLAXATIOX OF PTATE XXIX. 



All figures were drawn with the aid of the Abbe camera 

 lucida and with the Zeiss apochromatic objective 2 mm. aper- 

 ture 1.30, and compensating oculars 2, 4, 12, and 18. They 

 have been reduced in reproduction to 7/10 the size of the orig- 

 inal drawings. 



Fig. 1, Vertical longitudinal section of an entire cell, x 175. 



Fig. 2, Small portion of section similar to that showm in Fig. 

 1, showing distribution and structure of cell con- 

 tents, X GOO. 



Fig. 3, Portion of tangential section, x 1500. 



Fig. 4, Portion of tangential section, showing large spherical 

 nuclei, x 1500. 



Fig. 5, Procleavage stage, after disappearance of pyrenoids, 

 X 1500. 



Fig. C, Vegetative stage with large nuclei, irregular in out- 

 line, X 1500. 



Figs. 7-14, Successive stages of nuclear division, x 2250. 



Figs. 15-lG, Differe-nt parts of a single cell, showing successive 

 stages of nuclear division from one end of the cell 

 to the other, x GOO. 



Figs. 17-19, Spindles of unequal size, a. Multipolar spindles, 

 X 1500. 



Fig. 20, Unusual forms of figures of nuclear division, x 1500. 



Fig. 21, Irregular forms of nuclei, collected into groups, x 

 1500. 



Figs. 22-23, Early cleavage stages. Many nuclei with elon- 

 gated or pointed shapes, x 1500. 



