CHAP. II 



SPH.ERELLA 



241 



slow crawl when 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 



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

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

 (c. w) connected to cell-body by protoplasmic filaments, and flagella (ft). The 

 scale to the left applies to Figs. A D. 



B, resting stage of the same, showing nucleus (nu) with " nucleolus " (nu r ) 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 -eel Is. 



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, Sphterella lacustris, showing nucleus (nu), single large pyrenoid (pyr). and 

 contractile vacuole (c. vac). 



F, diagram illustrating the movement of aflagellum ; ab. its base : c, c\ c", different 

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



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. ZOOL. R 



