228 FRANK A HARTMAN. 



good with the exception of the chromosome form. The V- or 

 U-shaped chromosomes of young nymphs are shorter and thicker 

 than those of adults (see Figs. 33 to 47, Plate II.). 



In the second spermatocyte metaphase there is a repetition 

 of the size differences discussed in connection with the first 

 spermatocyte (see Figs. 48 to 55, Plate III.). In connection 

 with this it should be stated that almost invariably the cells of 

 the young nymphs were smaller than those of adults. 



(&) Comparison of Chromosomes of Different Cells of the Same 

 Individual. One of the most interesting conditions appeared 

 in different cells of the same individual. Chromosomes which 

 correspond as the number ones of the different cells show in many 

 cases variations in size (compare corresponding chromosomes of 

 the groups in: Figs. I, 3, 6, 8, 9, n, 14, 16; Figs. 2, 4, 5, 7, 10; 

 Figs. 12, 13; Figs. 17, 19, 22, 24, 25, 27, 30, 32; Figs. 18, 23; 

 Figs. 20, 21 ; Figs. 26, 28, 29, 31 ; Figs. 56, 57; Figs. 58, 59; Figs. 

 60, 61, 62, 63). In some instances this difference in size is very 

 striking (see .ones in Figs. 5 and 7; nines in Figs. 12 and 13; ones, 

 twos, and threes in Figs. 22 and 24; and many others which are 

 evident by a comparison of the figures). 



A great number of cells were studied to find whether this size 

 variation was exceptional. The variation was not unusual, but 



very common. 



The first spermatocyte anaphase presented like differences in 

 size (see Figs. 33, 35, 37, 39, 41, 43, 47; Figs. 34, 38, 40, 42). 



Chromosmes in the second spermatocyte metaphase show 

 similar variations (Figs. 48, 50, 55, 49, 51, 54). 



The second spermatocyte anaphase chromosomes are just as 

 variable (Figs. 64, 65, 66, 67). 



There is no doubt that corresponding chromosomes of the 

 same individual show a tendency to vary in size. This tendency 

 becomes more marked in certain cells. 



2. Causes of Chromosome Size Variation. 



(a) Unequal Growth.- During early prophase of the first 

 spermatocyte it is well known that the chromosomes appear as 

 groups of granules, which may be more or less clearly distin- 

 guished from each other. 



