LESSON IV 



EUGLENA 



The rain-water collected in puddles by the road-side, on 

 roofs, &c., is often found to have a bright green colour: 

 this is sometimes due to the presence of delicate water 

 weeds visible to the naked eye (Lessons XVL and XIX.), but 

 frequently the water when held up to the light in a glass 

 vessel appears uniformly green, no suspended matter being 

 visible to the unaided sight. Under these circumstances 

 the green colour is frequently due to the presence of vast 

 numbers of an organism known as Engk??a viridis. 



Although microscopic, Euglena is considerably larger than 

 either Haematococcus or Heteromita, its length varying from 

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

 middle and narrow at both ends (Fig. 5, 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 Haematococcus, 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 



