II 



PHYLUM PROTOZOA 



65 



small (microspores), others large (megaspores}. Their development 

 has not been traced ; but in all probability the micro- and mega- 

 spores are gametes and copulate in pairs. 



Symbiosis. In most Radiolaria there occur in the extra- 

 capsular protoplasm minute yellow cells (Fig. 44, z.), each enclosed 

 in a cell-wall, which multiply by fission independently of the 

 Radiolarian. It has been proved that these are unicellular organ- 

 isms, sometimes regarded as plants (Class Algae), sometimes as 

 animals (Class Mastigophora of the Protozoa), and named Zoo- 

 xanihettcB. This intimate association of two organisms is called 

 symbiosis : it is probably a mutually beneficial partnership, the 

 Radiolarian supplying the Zooxanthellse with carbon dioxide and 

 nitrogenous waste matters, while the Zooxanthellse give off oxygen 

 and produce starch and other food-stuffs, some of which must 

 make their way by diffusion into the protoplasm of the Radiolarian. 



l jr*t v.w-a'r: 



''rW Mrt*fc -?%# ... 



FIG. 48. Collozoum inerme. J. C, three forms of the entire colony, nat. size ; D, a small 

 colony showing the numerous central capsules (c. caps.) and extra-capsular protoplasm with 

 vacuoles (vac.) ; E, spores containing crystals (c.) ; F, mega- and micro-spore. (From 

 Biitschli's Protozoa, after Hertwig and Brandt.) 



Though the occurrence of symbiotic Algae is highly characteristic of the 

 Radiolaria, a similar association has been observed in various other Rhizopods, 

 notably in many Foraminifera. In the Radiolarian order Acantharia, 

 already referred to (p. 63), bodies long regarded as Zooxanthellse occur 

 mainly in the protoplasm of the central capsule ; but these have been shown 

 to be not symbiotes, but parts of the Radiolarian and devoid of cell-wall. 



APPENDIX TO THE RHIZOPODA. 



CHLAMYDOMYXA AND LABYRINTHULA. 



CHamydomyxa (Fig. 49), of which two species have been described, has been 

 found living on Bog-mosses (Sphagnum) in Ireland and in Germany and 

 Switzerland. It may occur either in the active or in the resting condition. In 

 VOL. I * 



