268 H. S. WILLIS. 



absence of the vacuole. Enucleated parts with the vacuole 

 apeared to behave in every way similarly to enucleated parts 

 without a vacuole. The same is true for nucleated parts. The 

 vacuole, therefore, cannot be reckoned as a determining factor 

 in the behavior of the fragments. 



Position Occupied by Fragments in the Intact Amceba. When 

 an amoeba is cut into two parts, the part containing the nucleus 

 may be from what was the anterior end or the posterior end of 

 the original specimen. The behavior was carefully studied in 

 25 parts, 13 from the anterior and 12 from the posterior end of 

 the intact individual. The results obtained are recorded in Table 

 I. No evidence was obtained indicating that the reaction of the 

 parts depends upon their location in the specimens from which 

 they were taken. The nucleated parts from the anterior end 

 responded precisely like those from the posterior end. Ob- 

 viously, then, the position in the intact specimen is not a 

 determining factor in the behavior of fragments. 



The Nucleus. We have demonstrated that parts of Amceba 

 which contain a nucleus behave essentially like normal specimens, 

 while those which do not contain a nucleus behave -quite differ- 

 ently, and that this difference in the behavior of the parts is 

 dependent upon neither their relative size, the presence of the 

 contractile vacuole, nor the location of the parts in the animals 

 which were cut to produce them. It must, therefore, in some 

 way, be related to the nucleus. This will be considered in the 

 following paragraphs. 



THE INFLUENCE OF THE NUCLEUS UPON ATTACHMENT. 

 Dellenger (1906) made it clear that attachment always accom- 

 panies and is essential to efficient locomotion in Amceba and 

 Difflugia. Twenty-five of my experiments on fragments of 

 Amceba, in which observations were made on attachment, 

 demonstrate quite clearly that nucleated fragments are usually 

 continuously attached to the substratum, and that enucleated 

 fragments are rarely attached. In these experiments some 

 specimens were observed for only ten minutes; others for a very 

 much longer period of time, the maximum being 72 hours. 

 Records of attachment or unattachment in all were made at 

 definite intervals. The following detailed description of the 



