ORIENTATION IN COLONIAL ORGANISM 



11 



great increase as they are brought back to the original position 

 again. If, then, the photo-sensitive tissue is largely confined to 

 this hyaline substance as it seems to be in Euglena, we should 



b. 



a. 



<- 



<- 



Fig. 6 Diagrammatic sketch representing the process of orientation in a 

 colony of Gonium as seen from the side.. Each circle represents a zooid; the 

 small arcs represent the eye-spots, the arrows the direction of the rays of light, 

 and a-b, Oi-fei, 02-62, etc., different positions assumed by the colony during the pro- 

 cess of orientation. Only 4 of the 16 zooids in the colony are shown. The colon j^ 

 rotates on its anterio-posterior axis as it proceeds. This causes the hyaline por- 

 tion of the eye-spot to become alternately fully exposed to the light and shaded. 

 The turning of the colony is due to an increase in activity of the zooids as they 

 are transferred to a position in which the hyaline part of the eye-spots is shaded, 

 that is, the positions represented by a, 61, «2, 63, etc. The hyaline part is probably 

 highly sensitive to light, and the increase in activity mentioned is probably de- 

 pendent upon the time-rate of reduction in illumination on this part. 



