108 BRUCE D. REYNOLDS. 



minute physiological differences even before these changes have 

 become expressed morphologically. Furthermore, the physio- 

 logical difference between two organisms, as indicated by this 

 method, appears to be more permanent and less subject to fluc- 

 tuations than certain morphological variations which have been 

 utilized by others. In some instances cross-fusion was observed 

 to take place readily between specimens belonging to the same 

 clone though they appeared quite different to the eye. In other 

 words: the physiological variations, as determined by means of 

 the ability or inability of an individual to fuse with a fragment 

 of protoplasm belonging to another, seem to be independent of 

 differences in size or shape of the two animals concerned. 



Fusion between cell-bodies and severed fragments has been 

 observed by the author in ten species of the genus Difflugia, in 

 Arcella poly pom, Centra pyxis aculeata, and also other forms of 

 protozoa. The phenomenon seems to be fairly common among 

 the thecamceba-. Perhaps it would be well to emphasize at this 

 point the fact that throughout these experiments any individual 

 Arcella would fuse with its own fragments (provided they were 

 not too far removed, or had not been separated for too long a 

 period) under any environmental conditions to which they were 



subjected. 



ACKNOWLEDGMENTS. 



This problem suggested itself to me while I was discussing 

 with Professor Wm. A. Kepner, the results of our work ('23) 

 Reactions between Cell-bodies and Pseudopodial Fragments of 

 Difflugia, I wish to express my deepest gratitude to Professor 

 R. \V. Hegner and Dr. Wm. H. Taliaferro, under whose direction 

 the work was done, for their valuable advice and criticisms. I 

 am also deeply indebted to Professor H. S. Jennings for reading 

 the manuscript and making some important suggestions. 



THE ORGANISM. 



The experimental animal used in this investigation was a mul- 

 tinucleated Arcella closely resembling the species described by 

 Penard ('85) as A . poly pom. Hegner ('20) worked with the same 

 organism, calling it A. polypora. However, in the same paper he 

 also gave measurements of a larger multinucleated form which 



