1 92 



JOHN* S. DEXTER. 



Now the supposition is that if two of the factors lie close together 

 on the same side of the double chromosome, they may escape 

 separation by the splitting. This means that the factors must be 

 closer together than half the distance around one complete turn of 

 the spirally twisted chromosomes. This length is the maximum 

 possible in order to allow two factors to be coupled on account 

 of proximity. This length might be indefinitely diminished so 

 that many factors of one of the parental chromosomes might lie 

 closely approximated on the same side of the split, and therefore 

 be coupled. 



In order to make the situation clearer to myself, I took two 

 pieces of one fourth inch rubber tubing, eighteen inches long, 

 and marked off, with ink, lengths of one inch. Each tube repre- 

 sented one chromosome of a homologous pair, and the inch 

 lengths represented the factors. I marked the factors on one 

 chromosome with odd numbers, I, 3, 5, 7, etc., to 35. This 

 chromosome I called maternal. The factors of the other I 

 marked with 2, 4, 6, 8, etc., to 36, and called this chromosome 



TABLE IX. 



The two vertical columns named r (right) and I (left) contain all the factors of 

 both parents. Each column represents one gamete and contains that half of the 

 factors not found in its fellow. Odd numbers represent maternal, even numbers 

 paternal characters. 



