214 INTRODUCTION TO CYTOLOGY 



upon the chromosome theory on the ground of amitosis have signally 

 failed. The results obtained by Sakamura (1920) in his study of modi- 

 fied mitosis in chloral ized plant cells are strikingly similar to those of 

 Conklin, and his conclusions regarding the chromosome theory are es- 

 sentially the same. 



From the foregoing it is evident that the problem of the effect of 

 amitosis upon the differentiation of the tissues in which it occurs and 

 upon the hereditary powers of the nucleus is by no means easy of solution, 

 and that much care must be used in interpreting supposed amitotic phe- 

 nomena in fixed preparations. The work of Conklin and Sakamura has 

 shown clearly that many of the phenomena reported as amitosis are in 

 reality aberrations of the mitotic process, and that the opinions of many 

 writers are undoubtedly due to a failure to recognize this fact. Should it 

 be proved, however, that true amitosis may occur in the lineage of 

 normally functioning germ cells a serious obstacle would be placed in the 

 way of the chromosome theory of inheritance in its current form, for this 

 theory requires that, no matter what happens in cells not in the direct line 

 of the germ cells, nuclear division in this line must be exclusively mitotic 

 in order that the hereditary mechanism in the nucleus shall be preserved. 

 This mechanism, as we shall see in later chapters, is supposed to be of 

 such a nature that amitosis would seriously derange its organization. 

 In each daughter nucleus of an amitotic division some of the elements 

 necessary for normal functional activity would presumably be lacking, 

 owing to the simple mass division of the chromatin. With reference to 

 this point it has been contended by Child that the nucleus is a dynamic 

 system capable of regenerating its lost parts and " producing a whole" 

 after amitosis. But it is a well established fact that when chromosomes 

 are lost in abnormal mitotic division they are not regenerated by the 

 daughter nuclei (non-disjunction; Chapter XVII). 



In this connection an experiment performed by Chambers (1917) is 

 of interest. This investigator succeeded in pinching the nucleus of an 

 animal egg into two pieces. The two " amitotic ' : nuclei so produced 

 reunited upon touching, after which the egg was fertilized and passed 

 through the early cleavage stages in the normal manner. It is known 

 that the character of these early stages is largely independent of the 

 nuclei present, being the outgrowth of an organization already present 

 in the egg cytoplasm. (See Chapter XIV.) The later stages, in which 

 the effects of the hereditary constitution of the nucleus appear, were not 

 reached in the present experiment. Moreover, the entire chromatin 

 outfit was present in the reunited nucleus, which is not supposed to be 

 true of a daughter nucleus of an amitotic division-. From this experiment, 

 therefore, it can only be concluded that whatever disturbance of the 

 spatial arrangement of the nuclear elements may have been caused by 

 the temporary separation of the nucleus into two parts, it had no serious 



