8o 



PROTOZOA 



The " yellow cells " of a symbiotic Flagellate or Alga, Zooxan- 

 thella, are embedded in the jelly of all except Phaeodaria, and 

 the whole ectosarc has the average consistency of a firm jelly. 



The pseudopodia are long and radiating, with a granular 

 external layer, whose streaming movements are continuous with 

 those of the inner network. In the Acantharia they contain a 

 firm axial filament, like that of the Heliozoa, which is traceable 

 to the central capsule ; and occasionally a bundle of pseudopodia 

 may coalesce to form a stout process like a flagellum (" sarco- 



FiG. 25. — Skeletons of Radiolaria. A, Dorataspis ; B, Theocomis. (After Haeckel.) 



flagellum "). Here, too, each spine, at its exit from the jelly, is 

 surrounded by a little cone of contractile filaments, the myophrislcs, 

 whose action seems to be to pull up the jelly and increase the 

 volume of the spherical body so as to diminish its density. 



The intracapsidar protojjlasm is free from Zooxanthella 

 except in the Acantharia. It is less abundantly vacuolated, and 

 is finely granular. In the Porulosa it shows a radial arrange- 

 ment, with pyramidal stretches of hyaline plasma separated by 

 intervals rich in granules. Besides the alveoli with watery 

 contents, others are present with albuminoid matter in solution. 

 Oil-drops, often brilliantly coloured, occur either in the plasma 

 or floating in either kind of vacuole ; and they are often 

 luminous at night. Added to these, the intracapsular plasm 

 ■contains pigment-granules, most frequently red or orange, pass- 



