RIENTATION IN COLONIAL ORGANISM 



9 



If the position of the source of light is changed after a colony is 

 oriented so that the rays strike the anterior surface obliquely, it 

 turns at once until the rays are again approximately perpendicu- 

 lar to this surface. The colony as a whole never turns in the 

 wrong direction. Orientation is direct. The process is essen- 

 tially the same as in Volvox. There is no indication of random 

 movements or trial reactions in the colony as a whole. 



The turning of the colony in the process of orientation is due 

 to an increase in the activity of the flagellae of the zooids farthest 

 from the source of light. The following evidence indicates that 



O 



o — um 



— -h 



Fig. 5 A, Sketch of the eye of the turbellarian, Ut. vulgaris prepared by 

 crushing a living specimen. After Wilhelmi (Taf. 15, fig. 4). 



B, Sketch of a cross-section of the eye of Amphioxus lanceolatus. After 

 Hesse (Taf. 24, fig. 8). 



C, Sketch of a cross-section of the eye of the turbellarian, Sabussowia diocia, 

 After Bohmig (Taf. 12, fig. 15) . It can readily be seen that in all of these animals 

 the eyes consist of two essentially different parts, just as do the eye-spots in 

 Gonium and Eudorina, but that there is considerable differentiation in each part 

 in the former while in the latter there is none that can be seen. 



