iv] GREEN CELLS OF CONVOLUTA 123 



cell a function similar to that which the otocyst 

 performs for the animal. Just as the granule of chalk 

 which is contained in the otocyst serves, by its gravi- 

 tational movements, to stimulate C. roscoffensis to 

 orientate itself, so may the pyrenoid, falling now this 

 way and now that, serve to stimulate the protoplasm 



A 



Fig. 21. The infecting organism an alga belonging to the Chlamy- 

 domonadineae seen under the high power of the microscope. 

 A^macrocyte. B = microcyte. C h I. = chloroplast (represented by 

 a reticulurn) occupying the greater part of the cell. Nuc.= 

 nucleus. St. = eye-spot, indicated in A, but not in B, in which, 

 however, it occupies a similar position. Pyr. = pyrenoid. The 

 four long threadlike projections represent the flagella. 



of the green cell to perform like movements of 

 orientation. 



If the green cells which have taken up their 

 position along the water-line are examined micro- 

 scopically, they are found to include many which are 

 in active movement. Each such cell resembles, in 



