84 



THE SMALLEST LIVING THINGS 



of propagation, serves as a renovating process whereby old struc- 

 tures are discarded and new ones are formed from the funda 



Fig. 50— REPRODUCTION TS A 

 RENOVATION PROCESS 



Uroleptus mobilis normally has eight macro- 

 nuclei; prior to division these nuclei fuse into 

 one; this then divides to form eight nuclei in 

 each of the daughter cells. M, macronucleus; 

 m, micronucleus 



From a photomicrograph by the author 

 Magnification, 600 



mental organization. With this renovation there is a renewed 

 potential of vitality, a characteristic of all young organisms. 



Cell division in some forms 

 of ciliates, as in some flagel- 

 lates, results in incomplete sepa- 

 ration of the daughter individ- 

 uals, thus giving rise to colonies. 

 Such aggregates of individuals, 

 colored green by symbiotic al- 

 gae* (chlorella) , may be en- 

 closed in a common jelly, as in 

 Ophrydium versatile, which in 

 streams of cold water may form 

 jelly-masses as much as a foot 

 in diameter. Or the daughter 

 individuals may remain con- 

 nected by stalks and form 

 arboroid colonies, such as Car- 

 chesium, Epistylis, and Zoo- 

 thamnium (Fig. 51). Muscle- 

 like fibres from the individuals 

 run down the stalks and the main trunk of Zoothamnium so 

 that a single stimulus causes a contraction of the entire colony. 

 Similar fibers traverse the individual stalks but not the main 



Fig. 51— AN ARBOROTD COLONY OF 

 EPISTYLIS UMBELLARIA 



This is one of the vorticella-like ciliated pro- 

 tozoa. Some, m, of the individuals are males; 

 some, M, are females 



After Grecff 

 Magnification, 160 



* See page 58. 



