May, 1915.] The Chromosome Mechanism. 517 



has one allosome and the female two, the highest efficiency char- 

 acter may appear to be transmitted only thru the male simply be- 

 cause the female cannot get the double dose of favorable allosomes 

 except from a male. It is probable also that there are sex-limited 

 characters whose factors are not in the allosome. In such cases 

 the male of female condition modifies the activity of the factor. 



Besides the segregating results due to normal cell divisions there 

 is, of course, the possibility of irregular segregations and the fusion 

 of parts of one chromosome with another. Irregularities in re- 

 duction and vegetative karyokineses may thus produce funda- 

 mental changes in heredity. Irregularities may be of three gen- 

 eral types. 



a. The chromosomes may be doubled from the previous 

 number of the species, probably thru failure of a reduction 

 division. 



b. Increase or decrease of the usual number may be brought 

 about by some of the chromosomes being left behind on the 

 spindle, or by the entire synaptic pair or the daughter halves 

 being pulled to one pole. 



c. Material from one chromosome may possibly be trans- 

 ferred to another when fused ends of two univalents are pulled 

 apart in the reduction metakinesis and material belonging to one 

 chromosome might also be detached and drawn into another 

 during the protochromosome stage of reduction. 



The question of the origin of an hereditary factor in a chromo- 

 some or the absolute loss of a factor involves a consideration of 

 the mechanism, and the chemical, physical and vital properties 

 of the chromosomes about which we know little or nothing at the 

 present time. But that the chromosome itself is a mechanism 

 apparently as complex in its own way as the nucleus itself is 

 revealed by the microscope even with present methods. What 

 further complications may exist until the larger chemical units 

 are reached can only be conjectiu"ed. There is also a possibility 

 that the mosaic arrangement of the chromosomes in the zygote 

 may influence the expression of hereditary factors and the arrange- 

 ment and adjustment of chromatin granules and any other struc- 

 tures present in the linin plasm may have something to do with 

 the peculiar hereditary properties or abilities manifested by li^'ing 

 matter. 



