VARIATIONS IN SOMATIC CHROMOSOMES. 37 



methods of analysis. The total of the chromosome lengths of 

 any two complexes in any one form may be quite different and 

 yet precisely the same relationship between pairs is maintained. 

 If the total lengths of the chromosomes of certain cells differ, for 

 example, by ten per cent, then the reduction of each chromosome 

 of the "longer" cell by this amount will faithfully reproduce the 

 length conditions in the shorter complex. In other words, any- 

 thing influencing the length of the chromosomes in a cell will 

 affect all proportionally. Consequently it can be readily under- 

 stood that though the total lengths may vary considerably the 

 interpair relationship remains constant. Data in support of 

 these statements has been recently published (Hance/iy). 



Since only the organization of certain chromosomes, and not 

 the amount of chromatin, is disturbed by fragmentation it does 

 not seem to me that the individuality is lost. It is true that 

 certain chromosomes no longer exist as they were but since all 

 the parts are retained intact in the complex the individuality 

 hypothesis, as understood today, would seem sufficiently broad 

 to admit these cases. 



The discovery of the relationships of the chromosomes during 

 the analysis of the unusual conditions just reported, is, I think, 

 of considerably greater importance than the conditions them- 

 selves. Chromosome pairs exist in the soma and in the germ cells 

 which are entirely comparable. When arranged according to 

 length these pairs form a graded series. Between each pair there 

 is a constant difference in length. These relationships exist in 

 several other forms I have studied and appear to be fundamental. 

 Besides presenting several new problems of chromosome be- 

 havior and organization, the constancy of these interpair re- 

 lationships affords a check on the accuracy of cytological work 

 and a basis for comparison with the work of others. 



BIBLIOGRAPHY. 

 Hance, R. T. 



'17 The diploid chromosome complexes of the pig, Sus scrofa, and their varia- 

 tions. Journ. Morph., Vol. 30, 155-222. 

 '18 Variations in the number of somatic chromosomes in Oenothera scintillans 



deVries. Genetics, Vol. 3, May, 225-275. 



Other papers of importance upon this subject are listed in the bibliographies of 

 these two publications. 



