OBSERVATIONS ON UNICELLULAR FORMS 



129 



can be seen of the structure Inside. The tests can however 

 be readily removed. If the cover-glass Is allowed to press 

 lightly on the organism It splits open and the cell within 

 with its prominent eye-spot and bright green color escapes. 

 All these forms react definitely to light; they are negative 

 in strong light and positive in weak. They orient quite 



Fig. 16. I. Trachelomonas hispida showing structure; cv, contractile vacuole; 

 t, dark brown test nearly opaque; s, spines on surface; n, nucleus; ch, chloroplast; 

 e, eye-spot. 



II. Different view of same specimen showing that the eye-spot is nearly cen- 

 trally located. Note rough edges of eye-spot and loose granules composed of same 

 material. 



III. End view of eye-spot. 



mm., projected scale. I and II drawn with camera as seen under oil immersion. 



IV. Sketches of specimens seen in the process of leaving the test preparatory 

 to fission. They frequently swim about in the naked elongated state for some 

 time. 



accurately and proceed on a spiral course much like Eu- 

 glena. It is remarkable how sufficient light to cause 

 a stimulation can get through the dense black tests of 

 some specimens. 



In the study of the reactions of these organisms they were 

 mounted in water under a large cover-glass which was sup- 

 ported by a thin ring of vaseline. In this way evapora- 

 tion was prevented. The specimens thus mounted lived 



