ETE-SPOT AKD ELAGELLUM IIS" EUGLENA TIEIDIS. 481 



(8) All those chlorophyll-containing motile cells which are 

 very sensitive to light contain an eye-spot. Many other organisms 

 which do not possess an eye-spot are sensitive to light, but not to 

 so high a degree. 



(9) If the explanation given in par. 5 is correct, we have 

 in Euglena an extremely simple form of light-organ, consisting 

 of a specialized sensitive portion of the cell — the enlargement on 

 the flagellum — and a light-absorbing pigment-spot in close con- 

 tact with it. 



EXPLANATION OF PLATE 32. 



The figures have been drawn, unless otherwise stated, with the aid of the 

 Camera lueida, and the y\th oil-immersion of Leitz or the 2 mm. 1'4 apert. 

 apochromatic objective of Zeiss and ocular 18. 



Fig. 1. Eye-spots from different individuals, showing the arrangement of the 

 pigment-granules. 



Fig. 2, Side view of the anterior end of a motile cell, showing the flagellum and 

 its enlargement in front of the eye-spot. This specimen was stained 

 in methyl-green and fuchsin for two hours, then washed in water and 

 mounted in dilute glycerine. The whole of the red colom' was washed 

 out, the flagellum and its enlargement were stained light green ; the 

 eye-spot was left brown. 



Fig. 3. This shows the attachment of the bifurcate base of the flagellum to the 

 dorsal wall of the excretory reservoir. The protoplasm formed a 

 slight projection at the point of attachment, and was slightly more 

 hyaline or refractive than the rest. 



Fig. 4. The flagellum is attached to the excretory reservoir nearer the base than 

 in fig. 3, and each of its arms is slightly expanded at the base. The 

 enlargement appears just at the place where the bifurcation begins. 



Fig. 5. A view of the anterior end of a cell as seen from below. 



Fig. 6. A slightly oblique view of the anterior end of a cell seen from above. 



Figs. 7 & 8. Two views of the same cell, showing the enlargement at some dis- 

 tance from the eye-spot. 



Fig. 9. A freehand sketch of a portion of a cell in the resting condition. The 

 excretory reservoir, the eye-spot, and the bifurcate base of the flagellum^ 

 and its enlargement are shown. 



