ii EUGLENA 251 



to one another, are liberated as gametes, and conjugate in 

 pairs to form zygotes (pp. 197, 237), each of which becomes 

 surrounded with a cell-wall, and after a time again under- 

 goes multiplication. 



We will now examine another small organism which is 

 often found in puddles and pools, frequently in such vast 

 numbers as to give the water a green colour. This organism 

 is known as Euglena viridis. 



Euglena is also microscopic, its length varying from 

 TTJ- mm. to \ mm. The body is spindle-shaped, wide in the 

 middle and narrow at both ends (Fig. 69, A E) : one 

 extremity is blunter than the other, and from it proceeds 

 a single long flagellum (fl] by the action of which the 

 organism swims with great rapidity, the flagellum being, 

 as in Sphaerella, directed forwards. Besides its rapid 

 swimming movements, Euglena frequently performs slow 

 movements of contraction and expansion, something like 

 those of a short worm, the body becoming broadened out 

 first at the anterior end, then in the middle, then at the 

 posterior end, twisting to the right and left, and so on (A D). 

 These movements are so characteristic of the genus that the 

 name euglenoid is applied to them. 



The organism consists of protoplasm covered with a very 

 delicate membrane or cuticle which is often finely striated, 

 and is to be looked upon as a superficial hardening of the 

 protoplasm. The colour is due to the presence of chloro- 

 phyll, which tinges all the central part, the two ends 

 being colourless. It is difficult to make out whether the 

 chlorophyll is lodged in one chromatophore or in several. 



In Sphrerella we saw that chlorophyll was associated 

 with starch (p. 243). In Euglena there are, near the 

 middle of the body, a number of grains of paramylum 

 (H, /), a carbohydrate of the same composition as starch 



