CHAP. II 



SPH/ERELLA 



241 



when divided by 300. It has been found that such 

 organisms as Sphrerella travel at the rate of one foot in 

 from a quarter of an hour to an hour; or, to express the 



FIG. 68. A, Sphczrella pluviacis, motile phase. Living specimen, showing 

 protoplasm with chromatophores (chr) and pyrenoids (far), cell-wall (c. iv) 

 connected to cell-body by protoplasmic filaments, and flagella (J?). 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, SphcErella lacustris, showing nucleus (nu\ single large pyrenoid (pyr), and 

 contractile vacuole (c. vac). 



F, diagram illustrating the movement of a flagellum ; ab. itsibase ; c, c', c". differ- 

 ent positions assumed by its apex. (From Parker's Biology : E, after Biitschli.) 



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 end is always directed 



PRACT. ZOOL. R 



