CHAP. II 



SPH.KKRLLA 



slow crawl \vhrn divided by 300. It has been found that 

 such organisms as Sphaerella travel at the rate of one 

 foot in from a quarter of an hour to an hour ; or, to 



C.W- 



FIG. 68. A, Spficerella pluvialis, motile phase (x about 350). Living specimen, 

 showing protoplasm with chromatophore (ckr) and pyrenoids (pyr), cell-wall 

 connected to cell-body by protoplasmic filaments, and flagella (fl). The 

 scale to the left applies to Figs. A D. 



B, resting stage of the same, showing nucleus (nu) with " nucleolus " (nu') and 

 thick cell-wall (c. w) in contact with the protoplasm. 



C, the same, showing division of the cell- body in the resting stage into four 

 daughter-cells. 



D, the same, showing the development of flagella and detached cell-wall by the 

 daughter-cells before their liberation from the enclosing mother cell-wall. 



E, Sphtzrella lacustris, showing nucleus (nu), single large pyrenoid lj>yr). an.l 

 contractile vacuole (c. vac). 



f, diagram illustrating the movement of a flagellum ; ab. its base : c , c', c", different 

 positions assumed by its apex. (From Parker'5 Biology; E, after Biitschli.) 



express the fact in another and fairer way, that they 

 travel a distance equal to two and a half times their 

 own diameter in one second. In swimming the pointed 



PRACT Z D 



