PHYLUM PROTOZOA 



63 



a firm gelatinous mass, the calymma or vacuolated extra- 



capsular protoplasm (D, vac.) common to the entire colony, 

 having embedded in it numerous central capsules (c. caps.) each 

 indicating a zooid of the colony. Collozoum may attain a length 

 of 3 or 4 cm. 



Reproduction by binary fission has been observed in some 

 cases, and is probably universal. The nucleus divides first, then 

 the central capsule, and finally the extra-capsular protoplasm. 



Spore-formation has been observed in Collozoum and some other 

 genera : the intra-capsular protoplasm divides into small masses, 

 each of which becomes a flagellula (Fig. 47, E, F) provided with a 

 single flagellum. In some instances all the spores produced are 



FIG. 47. Collozoum inerme, A 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(roc.) ; B, spores containing crystals (c.) ; F, mega- and microstore. (From Butschli's 

 Protozoa, after Hertwig and Brandt.) 



alike (E), and each encloses a small crystal (c.): in other cases (F) 

 in the same species the spores are dimorphic, some being small 

 (microspores), others large (megaspores). Their development has not 

 been traced. 



Symbiosis. One most characteristic and remarkable feature 

 of the group has yet to be mentioned. In most species there occur 

 in the extra-capsular protoplasm (in the intra-capsular in some 

 cases) minute yellow cells (Fig. 43, z.) which multiply by fission 

 independently of the Radiolarian. It has been proved that these 

 are unicellular organisms, sometimes regarded as plants (Class 

 Algae), sometimes as animals (Class Mastigophora of the Protozoa), 

 and named Zoochlorellce. This intimate association of two organisms 

 is called symbiosis : it is probably a mutually beneficial partner- 

 ship, the Radiolarian supplying the Zoochlorellaa with carbon 

 dioxide and nitrogenous waste matters, while the Zoochlorellse 



