VARIATIONS IX THE SIZE OF CHROMOSOMES. 23! 



We have the right to assume that some chromosomes within 

 the cell have greater influence in determining the characteristics 

 of a new individual, otherwise they would all have equal power 

 in this respect, which is inconceivable. Especially is this so 

 when we see the great difference in the size of chromosomes within 

 the same cell because there must be some purpose in this if the 

 chromosomes are so important. 



Naturally the larger chromosomes would represent larger 

 groups of characters or else power to make the characters, which 

 they determine, more prominent. 



By a variation then in size of any one chromosome either the 

 number or the intensity of the characters, which it represented, 

 would be varied. If the chromosome is increased, its influence 

 in the determination of the characteristics of the offspring would 

 also be increased. 



Knowing that the offspring from the same parents show con- 

 siderable variation in their characteristics and having found that 

 corresponding chromosomes of the same animal vary in size it 

 seems probable that we have in this the cause of continuous 

 variation. 



According to this theory if an immature animal were mated 

 with one of maturity, on account of the smaller size of its germ 

 cell chromosomes (shown in the first portion of this paper) the 

 immature germ cell would be overshadowed by the mature germ 

 cell in the determination of the characteristics of the resulting 

 offspring. In many cases this seems to be true though it is 

 difficult to obtain trustworthy data. 



V. CONCLUSION. 



1. Germ cell chromosomes of very young nymphs are smaller 

 than those of adults; this difference bears a direct relationship 

 to the size of the germ cells. 



2. As a result of either unequal growth or unequal division, 

 corresponding chromosomes of different cells within the same 

 individual vary in size. 



3. The theory suggested by the observations in this paper is 

 that the variation in the size of corresponding chromosomes of 

 germ cells is the cause of continuous variation among animals. 1 



1 The author is indebted to Dr. C. E. McClung for criticism. 



