May, 1918.] A Cycological Life Cycle. 145 



ing would liave borne the same chromosome combination as their 

 parents. The combination diagramed could never be repeated 

 until egg and sperm containing between them the chromosomes 

 represented by all four symbols met and in the resulting zygote 

 the chromosomes were oriented on the spindle in exactly the 

 proper manner and this was followed by a succeeding fertilization 

 by pure gametes bearing respectively only dotted and crossed 

 chromosomes. Thus in an organism with four chromosomes in 

 the diploid generation there are no less than nine possible chromo- 

 some combinations, while • in organisms with numerous chro- 

 mosomes the number of combinations possible is 3" where n is the 

 number of chromosomes. 



Without making an\^ specific assumptions concerning dif- 

 ferences in specific maternal and paternal chromosomes other 

 than the common knowledge that the plasms of the two parents are 

 in a general way different in heterozygous organisms, it is evident 

 that there is here a mechanism varied enough to account in large 

 measure for the large variability in inheritance which is so familiar 

 No two children of the same parents (except identical twins) are 

 ever alike, be the family ever so large. When we take account of 

 intermarriage even without considering A^arying racial char- 

 acteristics it is not surprising that we never find two faces alike. 



If however we assume that the long crossed chromosome for 

 example bears a specific character which is absent from its mate 

 the long dotted chromosome, it will be seen that any one of four 

 possible combinations with respect to this one chromosome and 

 the character it bears may be reaHzed in fertilization: (1). i\n 

 egg bearing the x chromosome may be fertilized by a sperm 

 bearing an x chromosome or, (2), by a sperm bearing a dotted 

 chromosome, (3), an egg bearing a dotted chromosome may be 

 fertilized by a sperm bearing an x chromosome or (4), by a sperm 

 bearing a dotted chromosome. In the first case all of the cells 

 produced in the subsequent reduction would bear the x chromo- 

 some together with its character, and if inbred would continue 

 pure ever after. In the fourth case the oft'spring would be pure 

 in respect to the dotted chromosome and whatever characters 

 it might carry, while in the second and third cases it would be 

 mixed. This is, however, nothing more or less than a statement 

 of Mendel's Law. 



