20 



Marvels of Pond-Life, 



the stage, and having all the centre of its face covered 

 with a plaster of black silk. In this method the cen- 

 tral or direct rays from the mirror are obstructed, but 

 those which strike the edge of the bull's-eye are bent 

 towards the object, which they penetrate and illuminate 



Vorticella, with posterior Vorticella in process of self-division, 



circlet of cilia in process of A new frontal wreath in formation in 

 separation,300 linear. Stein. each of the semi-lunar spaces. 



if it is sufficiently transparent and refractive. Another 

 mode of dark ground illumination is by employing an 



