OBSERVATIONS ON UNICELLULAR FORMS 91 



cisely what factors are involved in causing the forward 

 movement I was not able to ascertain. Only very slight 

 contractions can be seen at any time and no streaming 

 movements at all. 



The posterior end is in much closer contact with the sub- 

 stratum than the anterior. If currents of water are passed 

 back and forth over the Euglenae it can be seen that the 

 anterior end is free, for it moves with the current. Fre- 

 quently specimens are found attached to the slide with 

 only the tip of the caudal spine in contact with the sur- 

 face. In such specimens the whole body sw^ings about with 

 the current. They are held fast by an adhesive substance 

 which they secrete. The presence of such a substance can 

 be detected by passing a small glass rod across the path of 

 a crawling individual near its posterior end, or by pushing 

 the rod about on a slide containing numerous Euglenae 

 which have been crawling about for a short time. If this 

 is done the end of the rod soon becomes covered with a 

 substance to which cling numerous Euglenae attached 

 usually only at the posterior end. It is however not likely 

 that the extrusion of the secretion forces the Euglenae along, 

 as is supposed to be true in the case of diatoms. The body 

 appears to become alternately more and less curved as they 

 rotate in such a way as to force them forward. The caudal 

 spine appears to be used as a sort of lever in this movement. 

 They can however move without the use of the spine, for 

 moving specimens were repeatedly seen in which the point 

 of the spine was not in contact with the slide at all. This 

 was evident especially in specimens which rotated only 

 partially over and then back again. 



As these creatures crawl along, rotating on the long axis 

 with the anterior end progressing on a spiral course, the 

 dorsal surface, the surface containing the eye-spot, always 

 faces the axis of the spiral. This is just the opposite of 

 Jennings' observations on Euglena viridis in the free- 

 swimming state. I found however that E. acus and a 

 few other species swim with the dorsal side facing the axis 



