ELMER L. SHAFFER. 



structure of theory must remain as unwieldy as at present" 

 (Kingsbury, '12, p. 48). As I have before pointed out, it is 

 possible that we may find an explanation for such movements of 

 the chromatic elements in the linin ground-work of the nucleus. 

 Homologous chromosomes have linin connectives running be- 

 tween them and it is possible that their union in synapsis is 

 brought about by a contractility of these interchromosomal linin 

 fibers, very much as the spongioplasm acts in localizing substances 

 in the egg (Conklin, '17). The linin is, therefore, the persistent 

 material of the nucleus, while the chromatin may be variable 

 in amount in certain phases of the cell-cycle. 



(&) Mitochondria. The function or the role of the mitochon- 

 dria in the cells of animals and plants still remains one of the 

 unanswered cytological problems of to-day. A few cytologists 

 have insisted that the mitochondria are idioplasmic materials 

 which have a role in the transmission of hereditary characters 

 similar to the chromosomes. According to this view, the chro- 

 mosomes bear the determiners for the generic or racial characters 

 of the organism, while the mitochondria bear the determiners 

 for the specific or individual hereditary characters. From what 

 little we do know of "cytoplasmic inheritance" it seems that the 

 reverse is true (Conklin, '17) and that the larger orientations 

 of development are fixed by the cytoplasm, particularly that of 

 the egg. The idioplasmic view of the mitochondria was de- 

 veloped from the fact that they were found in all cells at all 

 times and that they behaved characteristically during mitosis, 

 becoming equally distributed to the daughter cells. These facts 

 seemed to indicate a persistence and continuity of the mito- 

 chondrial substance through the cell-cycle which would fit in 

 with the view of their idioplasmic nature. As I have before 

 indicated (p. 445) there is no basis for maintaining their genetic 

 continuity, but rather that "new" mitochondria may be formed 

 in the cell without any relation to previously existing mito- 

 chondria. 



According to another view the mitochondria may become 

 transformed into certain histological elements of the cell, such 

 as muscle and nerve fibrillte, collagenic fibrils, and certain of 

 the glandular secretions (pancreas, thyroid, etc.). Without 



