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



This peculiarity has been carried a step further in Difflugia, for 

 we find that in distantly related individuals of the same species the 

 protoplasm has become so modified in an individualistic way that 

 fusion will not take place between them. Loeb (1920) has re- 

 corded observations on the power of tissues to exhibit different 

 reactions to different degrees of family relationship. Our experi- 

 ments suggest a similar ability on the part of Difflugia. 



Summary. 



1. In Difflugia separated pseudopodial fragments are recovered 

 by their cell-bodies, as evidenced by over one hundred experi- 

 ments. The species included in these observations were: D. 

 acuminata, D. corona, D. pyriformis, D. spiralis, and D. vulgaris. 

 The distances by which the fragments and their cell-bodies were 

 separated ranged from a few micra to 1,500 micra. The unfavor- 

 able conditions under which reunion does not occur are: (a) In- 

 jury to cell with consequent failure on its part to extrude pseudo- 

 pods; (&) separation from fragment by too great a distance; (c) 

 evaporation of water before completion of reactions. 



2. The severed fragments are not recovered as food, but enter 

 again immediately into the protoplasmic structure of the cell-body. 

 Such fragments are not reappropriated after they show visible 

 signs of death. 



3. In our observations fusion never occurred at the ends of 

 pseudopods, but always took place along an extended mid-region. 

 This indicates a physio-chemical difference between the ends and 

 the middle of such pseudopods. 



4. In some cases the severed fragments, which were only ecto- 

 plasmic in composition, were observed to take an active part in 

 restitution. Not only did they move toward, but apparently 

 shifted, their line of approach to correspond with the changing 

 positions of their cell-bodies. 



5. Fusion has not been observed to take place between two 

 enucleated fragments, even though they be placed in contact. 



6. Fusion between an individual of one species and a fragment 

 from an individual of a different species has not been observed. 

 The phenomenon seems to be specific. 



