NOTES AND LITERATURE 



HEREDITY 



A subject of vital importance to the theory of heredity is the 

 behavior of the chromosomes during the life history of the cell, 

 and especially during the process of cell division. This subject 

 has received an enormous amount of attention from investigators 

 but there is far from unanimity amongst eytologists as to the 

 actual phenomena of cell division, not to mention the signifi- 

 cance of these phenomena. Realizing that the heterotypic di- 

 vision in gametogenesis is the critical point in the life history of 

 the organism, so far as the theory of heredity is concerned, at- 

 tention has been concentrated very largely on this division. 

 This is in some respects unfortunate. A good many investigators 

 who have studied this division have attempted to interpret the 

 phenomena observed without full knowledge of the behavior of 

 the chromatic elements in ordinary somatic divisions, and have 

 attributed to phenomena observed in the heterotypic division 

 very special meaning for inheritance, when these same phenom- 

 ena are regular occurrences in all divisions, and hence are to be 

 interpreted in their relation to growth rather than to reproduc- 



The writer is not a cytologist, and realizes fully that his 

 opinions on cytological questions will not be regarded seriously, 

 especially by those who have worked at problems of this char- 

 acter until they have gotten fixed in mind certain theories as to 

 the meaning of the phenomena observed. Nevertheless, he has 

 given careful attention to published results of investigations of 

 this character, and has been driven by study of these results to a 

 particular interpretation of the principal phenomena reported. 

 It has seemed to me for some years that the double spireme so 

 often reported in the heterotypic division, and so often inter- 

 preted as a conjugation of homologous chromatin elements, al- 

 though this double spireme occurs in somatic divisions appar- 

 ently quite as generally as in the heterotypic, is nothing 

 more than the expression of a division of chromosomes which 



really occurs at least ; 



the resting stage following the 



previous nuclear division. It appears that this division may 

 begin at an even earlier period. 



