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



place, for care has been taken to place the animals in such positions 

 that this could be determined. Some substance may emanate from 

 each Difflugia, as products of its individual metabolism, which 

 furnishes the required stimulus. 



An interesting feature of the reaction between an ectoplasmic 

 fragment and its cell-body is presented by the fact that fusion has 

 never been observed to take place at the tip of an advancing 

 pseudopod, nor at its base, but always along an extended mid- 

 region. This suggests that the ends of such pseudopods must be 

 different from their sides. This, if well founded, carries the 

 analysis of pseudopodial formation a bit beyond that presented by 

 Hyman (1917), who showed that the younger pseudopods of an 

 amoeba have a different metabolic gradient from the older ones. 



The ability of enucleated fragments to react to stimuli has been 

 observed by others. Hofer (1889) showed that fragments of 

 amoebae lived for fourteen days ; their movements were carried on, 

 though somewhat modified. Verworn (1889) found that enu- 

 cleated fragments of Amoeba, Difflugia, Lachrymaria, Polysto- 

 mella, and Thalassicolla live a long time and perform normal move- 

 ments and normal reactions to stimuli. Minchin (p. 210) makes 

 this statement : " Non-nucleated fragments may continue to live 

 for a certain time ; in the case of amoeba such fragments may emit 

 pseudopodia, the contractile vacuole continues to pulsate, and acts 

 of ingestion or digestion of food that have begun may continue; 

 but the power of initiating the capture and digestion of food 

 ceases, consequently, all growth is at end, and sooner or later all 

 non-nucleate bodies die off." Lynch (1919) observed that enu- 

 cleated fragments of an amoeba may move, respire, digest, respond 

 to stimuli, and exhibit any activity which is dependent solely upon 

 katabolic or destructive processes of protoplasm. The group of 

 phenomena which they never show constitutes such processes as 

 growth, regeneration, and division. Willis (1916), on the other 

 hand, records that parts without a nucleus do not react as well as 

 nucleated portions — for example : they do not orient with reference 

 to a beam of light. Finally, Mast and Root (1916) say that "the 

 fact that enucleated parts of amoeba do not respond at all or 

 respond in a haphazard fashion indicates, as Hofer ('90) con- 

 cludes, that the nucleus acts as a regulatory center." Hofer, 



