30 



WM. A. KEPNER AND B. D. REYNOLDS. 



IV. Does the Fragment Take an Active Part in 

 Restitution ? 



If fusion between a cell-body and its fragment is true restitution 

 as has been claimed, one should not be surprised to see the frag- 

 ment taking an active part in the process. With this in view, 

 especial attention was given to the movements of fragments. 

 Without some object to mark the original positions, it is very easy 

 to confuse distances traveled by each body when two are approach- 

 ing each other. Therefore, when observations were made without 

 the use of a camera lucida to plot the positions, care was taken to 

 avoid falling into this error. Whenever fusion took place, the 

 protoplasm constituting the fragment seemed to flow into, and 

 commingle with, the protoplasm of the cell-body. But it was not 

 always possible to observe an appreciable movement on the part of 

 a fragment toward its cell-body before contact was made. How- 

 ever, on many occasions this could be seen. The two following 

 accounts are typical of the more striking reactions of this sort : 



On November 28, 1919, a fragment was cut from a Difflugia 

 spiralis, after which the cell-body was moved 1,500 micra distant. 

 Immediately after separation the fragment had the shape of an 

 elongated ovoid, then its contour changed continually for the next 

 thirteen minutes (Fig. 5 — 3, 4, 5, 6, 7, 8, 9, etc.). Each figure 

 represents the number of minutes that had elapsed since the opera- 

 tion took place. During the first twelve minutes its movement 

 seemed to be indefinite, as indicated in the diagrams, but by this 

 time the cell-body had advanced until the end of its nearest pseudo- 

 pod was within 150 micra of the fragment. From this time there 

 was a decided movement on the part of the fragment in the direc- 

 tion of the cell-body. As soon as the fragment had come within 

 reach of the long pseudopod, which the cell-body was extruding, 

 movement by the latter slowed down, and the distal end of the 

 pseudopod was lifted. Under this the fragment passed. The 

 fragment continued the approach, and two minutes from the time 

 it had come within the radius of the animal's pseudopod it had 

 traveled about twenty micra and reunited with its cell-body (Fig. 

 5 — A, a, b, c, and d). 



On November 8, 1919, a large fragment was cut from a pseudo- 



