OTHER PROTOZOA 87 



Reproduction. Reproduction in Euglena takes place by 

 binary longitudinal division (Fig. 39 E). The nucleus divides 

 by a primitive sort of mitosis. The body begins to divide at the 

 anterior end. The old flagellum is retained by one half, while a 

 new flagellum is developed by the other. Often division takes 

 place while the animals are in the encysted condition. One cyst 

 usually produces two Euglena although these may divide while 

 still within the old cyst wall, making four in all, while recent 

 observers have recorded as 

 many as thirty-two young 

 flagellated Euglena which 

 escaped from a single cyst. 



Behavior. Euglena swims 

 through the water in a spiral 

 path. The effect of this 

 course is, as we found in 



Paramecium (p. 64), the pro- r -p.. 



c TIG. 41. Diagram showing the reaction 



duction of a perfectly straight of EugletUB to light . The light comes 

 course through the trackless from the direction indicated by the 

 water. When stimulated by arrows, while the opposite side of 



a change in the intensity of the vessel is shaded > as indicated 



,, r T, ^ 7 . ,, by the dots. The Euglence gather 



the light, Euglena, in the ma- *.* j- * 



in the intermediate region across the 



jonty of cases, stops or moves middle. (From Jennings.) 

 backward, turns strongly to- 

 ward the dorsal side, but continues to revolve on its long axis. 

 The posterior end then acts as a pivot while the anterior end 

 traces a circle of wide diameter in the water. The animal may 

 swim forward in a new direction from any point in this circle. 

 This is the avoiding reaction (Fig. 40). 



Euglena is very sensitive to light and is a favorable object for 

 the study of phototropism. It swims toward an ordinary light 

 such as that from a window, and if a culture containing Euglena is 

 examined, most of the animals will be found on the side toward 

 the brightest light. This is of distinct advantage to the animal, 

 since light is necessary for the assimilation of carbon dioxide 



