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 (Lesson XVI.), 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 Euglena viridis. 



Although microscopic, Euglena is considerably larger than 

 either Haematococcus or Heteromita, its length varying from 

 ^ mm. 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 (_/?) by the action of which the 

 organism swims with great rapidity, the flagellum being, 

 as in Hsematococcus, 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 



