Chromatin as ""Hereditary Substance^'' ^^iTl 



into tlie structure and maneuvering of the chromosomes of 

 the germ-cells during the "ripening" of the germ-cells. The 

 facts usually taken as the starting point for the hypothesis 

 are that all the cells, both body and germ, of an ordinary 

 sexual plant or animal have a constant number of chromo- 

 somes, the number being characteristic for the species ; that 

 before fertilization, an essential feature of which is the 

 union of male and female chromosomes, the chromosome 

 number of both male and female cells is reduced by one half, 

 excepting in those cases wliere there is an odd or accessory 

 chromosome, so that the union of the chromosomes in ferti- 

 lization restores the number typical of the species ; that the 

 final adjustment gives the fertilized ^gg and all the cells 

 arising from it supposedly equal portion of chromatin from 

 each parent ; and finally, that the chromosomes of the germ- 

 cells in many animals, if not in all, are not all alike either 

 in form or size. 



Proceeding from these facts Sutton studied the germ-cells 

 of the lubber grasshopper with reference to the question of 

 wliether the differences in size and form of the chromosomes 

 are haphazard and meaningless or have some constancy, 

 especially in relation to their maternal and paternal sources, 

 and in the way they couple with one another in fertilization. 

 Summarizing the results for the germ-cells as they grow 

 and multiply before the ripening process sets in, he con- 

 cluded that during this period the chromosome group of 

 each germ-cell is composed of two equivalent chromosome 

 series, each series consisting of eleven chromosomes differing 

 among themselves in size, and that in all probability one of 

 these series comes from the father and the other from the 

 mother. Furthermore, he believed that the reduction in 

 number which takes place in this ripening stage and is known 

 as synapsis, is accomplished by the union of two series in 

 such fashion that each member of the maternal series unites 

 with one of corresponding size, its mate of the paternal 



