56 ORGANISMS OF ONE CELL 



motile apparatus for the pair. Fusion of nucleus and cell body 

 continue until a single cell results. This then secretes a mem- 

 brane and becomes quiescent, or it divides and behaves like an 

 ordinary individual. Here there is typical fertilization but no 

 difference between the conjugating cells so far as can be de- 

 tected (Fig. 22). 



Allied Forms. Many hundreds of species of flagellated pro- 

 tozoa are known and may exhibit the most manifold variations 

 in structures and functions. Many of them have only one 

 flagellum as Peranema or Euglena for example, which are com- 



"^K.^;^^^ *^>*^ o ^ 



FIG. 24. Uroglena americana, a colony of flagellated protozoa in which the indi- 

 viduals are embedded in a common gelatinous matrix. 



mon organisms in infusions of different kinds. It is a remark- 

 able and fascinating sight to see a relatively large cell like Pera- 

 nema drawn steadily forward by the undulations of the tip of 

 its long and easily seen flagellum. In this case the entire 

 flagellum does not vibrate, but only the tip, whereas in Euglena 

 the whole flagellum is in constant motion and is almost impossi- 

 ble to see. 



Nutrition in Peranema, as in Chilomonas is saprozoic, but it is 

 entirely different in the case of Euglena which has the power to 

 manufacture its food in the same way that the higher green.plants 

 do. This holophytic nutrition is accomplished through the 

 agency of chloroplastids or color-bearing structures distributed 

 throughout the protoplasm of the Euglena cell (Fig. 21). The 



