The Protozoa 



151 



and also a distinct flagellum. It is, therefore, able to creep about on 

 a solid object, or swim directly through the water. 



Chilomonas ( ' ) is a very common flagellate in 



laboratory cultures. Uroglena forms spheroidal colonies consisting of 

 a great number of individuals held together by a gelatinous matrix. This 

 form is often responsible for the "oily odor" of drinking water, caused 

 by the escape of small droplets of an oily substance from the cells. 



Volvox ( ) (Fig. 49) is a colonial flagellate 



found in fresh-water ponds. It may'consist of as many as twelve thou- 

 sand cells. Protoplasmic strands connect each cell with those that sur- 

 round it ; physiological continuity is thus established. All of the cells 

 are not alike, since some of them, the germ cells, are able to produce new 



Fig. 68. 



Proterospongia haeckeli S. K. 

 (S. Kent.) 



Fig. 69. 



A. Peredinium divergens, chr. 



B. _ Ceratium tripos (Calkins). (From Pratt's "Manual" by 

 permission of A. C. McClurg & Co.) 



colonies, while others, called somatic or body cells, have no reproductive 

 power. 



Some of the germ cells, the parthenogondia ( ), 



grow large, divide into many cells, drop into the center of the mother 

 colony, and finally escape through a break in the wall. Other germ 



Noctiluca millaris. A, entire animal; f, flagellum; n, nucleus; o, cytostome 

 and beside it the tooth and lip; t, tentacle; B, C, upper end with two stages in 

 the formation of zoospores; D, zoospores. (After Hertwig.) 



