146 



LIGHT AND THE BEHAVIOR OF ORGANISMS 



zooids, owing to the rotation of the colonies on the long 

 axis and the consequent transfer of the zooids from the 

 illuminated to the shaded side. This response is similar to 

 the avoiding reaction in Euglena, Trachelomonas, Chlamy- 

 domonas and other unicellular forms. 



If Bancroft is correct in his description it is evident that 

 the factors involved in orientation in a galvanic current 

 and in light are not the same, and that the orienting reac- 

 tions in light are not tropic according to Loeb's definition. 



2. Pandorina and Eiidorina 



These organisms are much like V^olvox in structure. 

 They are however very much smaller and contain only 



-0.1 mniT 



Fig. 21. I. Eudorina; II, Pandorina, showing structure and form; a, anterior 

 end; z, zooids; ch., chloroplasts, all the zooids are well filled with them; e, eye- 

 spots — note difference in size at opposite poles, and location on outer posterior 

 surface of zooids. Each zooid has two flagella, — only a few of them are repre- 

 sented. Eudorina is surrounded by a hyaline layer the outline of which is repre- 

 sented by a dotted line. Outlines made with camera; mm., projected scale. 



III. Ej'e-spot greatly magnified; n, surface view; m, side view. The flat surface 

 is directed outward and slightly posteriorly. 



from 32 to 64 zooids (Fig. 21). By means of methods 

 similar to those used in studying Volvox it was found that 



