504 T. H. Morgan. 



In the middle pieces its amount is greatest at the middle. In the 

 posterior pieces the amount is greatest nearer the anterior end. 



These relations throw more light on the problem of localiza- 

 tion in regeneration than any others that I know of, and the con- 

 clusions to be drawn from them are so obvious that they can 

 scarcely fail to carry conviction. 



The reader may probably have observed that in the preceding 

 attempt to account for the phenomena of polarity I have referred 

 to the protoplasm in the sense of cytoplasm rather than nucleus. 

 Yet on the current view of embryologists every nucleus contains 

 the sum total of all the hereditary qualities and may transfer, in 

 some unknown way, these qualities to the protoplasm. Every 

 part, therefore, is looked upon as potentially totipotent, and its 

 only limitations are those due to its protoplasmic differentiation. 

 Even this is supposed to be capable of being worked over under 

 the influence of the nucleus so that it may at times return to its 

 "embryonic condition" of indifference and may then under the 

 influence of the nucleus again be differentiated in new ways. 

 If this belief represents the actual conditions in the tissues then 

 the remarkable limitations of regenerative power in some instances 

 can only be explained by assuming that the protoplasm when once 

 differentiated can in these cases no longer return to the so-called 

 "embryonic condition." It is not apparent, if this be the case, 

 why nuclei should always be present in somatic cells unless they 

 have some other important function to perform than that of 

 transmitters of hereditary qualities. There is, of course, much 

 evidence to show that the nuclei have important physiological 

 functions to perform, viz., in connection with the metabolism of 

 the cell. This admission at once raises the question as to whether 

 the main function of the nucleus may not be connected with 

 metabolism and have nothing to do with hereditary transmission, 

 unless indirectly. 



If we inquire on what evidence the accepted view rests that the 

 nucleus is the transmitter of the hereditary qualities we shall find 

 the evidence not entirely conclusive. The principal argument 

 in favor of this doctrine is that the spermatozoon brings into the 

 egg only, or mainly, the nucleus of the male germ-cell, and thus 

 the paternal qualities must become transmitted to the offspring 

 by means of the nucleus. It is pertinent to ask what becomes 

 of the cytoplasm of the male germ-cell .? Is the nucleus simply 



