254 H - s - WILLIS. 



Gruber (1912) found that parts of Am&ba proteus containing 

 a nucleus behave very much like normal specimens, but that 

 parts without a nucleus behave very differently; yet, in spite of 

 this, he held that the nucleus in general has no influence upon 

 protoplasmic movement. Hofer (1890) in observations on the 

 same species, obtained results similar to those of Gruber. He 

 asserts (p. 118) that movements in the parts with the nucleus 

 are similar to those in normal specimens, as are also those in the 

 other parts for a period of 15-30 minutes after division, but that 

 later the movements in the parts without a nucleus differ from 

 those in normal specimens in rate of locomotion, in regularity 

 of movement, and in the number and length of pseudopods. 



Hofer holds that these differences might be considered to be 

 due either to the injury received during the operation or to the 

 influence of the nucleus. But he maintains that, since any 

 injury sustained from the operation affects both fragments alike, 

 the operation could not be considered the cause of the observed 

 difference in behavior. He consequently concludes that the real 

 cause is to be found in the nucleus. He holds, however, that the 

 influence of the nucleus may be conceived to be direct or indirect; 

 that is, that behavior may be due to an impairing of the elemen- 

 tary functions (such as digestion, respiration, and excretion) 

 controlled by the nucleus. But Hofer found that the process 

 of digestion in the absence of the nucleus continues for several 

 days after division; that respiration takes place in the absence 

 of the nucleus; and that excretory functions in enucleated 

 segments continue till death. He therefore comes to the con- 

 clusion that the nucleus secretes a chemical substance and that 

 behavior is controlled through this. He thinks a certain amount 

 of this substance is stored up in the different parts of the proto- 

 plasm, and that the normal movement of the enucleated seg- 

 ments for 15-30 minutes after the operation is due to the influence 

 of the substance thus stored. Hofer maintains that, since 

 movement occurs in parts without a nucleus, cytoplasm has the 

 power of movement; but since the movement in these parts is 

 more irregular and haphazard than it is in nucleated parts, he 

 holds that the nucleus must have a regulatory function. In 

 other words, he thinks the nucleus serves as a regulatory "cen- 

 trum" for behavior. 



