CHROMOSOME STUDIES 189 



these six pairs, two (nos. 6, 6 and 5, 5) are more than twice the 

 length of any other pairs. Nos. 4, 4 and 3, 3 are the inter- 

 mediate pairs, the larger being about one-half that of no. 5 

 and less than one-half that of no. 6. Nos. 1, 1 and 2, 2, the 

 smallest pairs, are easily- distinguishable from nos. 3, 3 and 4, 

 4 and usually from each other. The sex chromosome is desig- 

 nated by 2x in this species because it ranks second in the total 

 series. It is distinguished from the ordinary chromosomes 

 numbered 2 by the addition of x. In general we have among 

 the ordinary chromosome pairs three distinguishable size-groups : 

 one embracing the largest (nos. 6 and 5), another the intermediate 

 nos. 4 and 3), and a third the smallest (nos. 2 and 1). These 

 three groups may be recognized in all the species of the family 

 here studied. There is noticeable, as the measurements will 

 later indicate, considerable difference in size between the two 

 largest pairs, very little between nos. 4 and 3, but again quite 

 an appreciable difference between nos. 2 and 1. 



The size relations are more evident, though not as accurately 

 shown, in the maturation divisions, and are best seen in views 

 of division figures perpendicular to the axis of the spindle. In 

 the Tettigidae the first maturation division is reductional. 

 The members of each pair of chromosomes appear on the first 

 maturation spindle attached to each other by distal ends only. 

 This gives, exclusive of the accessory chromosome, six rods 

 somewhat constricted, or even pulled apart, in the middle (figs. 

 29-34), Here again the six pairs may be grouped into three 

 sizes, the extremely large (6 and 5), the intermediate (4 and 3), 

 and the smallest (2 and 1). 



The inequality in the size of 6 and 5 is well marked, shown by 

 the 5's usually being more advanced in the act of separation 

 than the 6's (figs. 29, 30, 31, 33). This character holds for the 

 species of Acridium in distinction from those of Tettigidea, 

 where it is only slightly marked. It also holds in Parattettix, 

 though not to so great a degree. 



The 3's and 4's are more nearly alike in size than the 5's and 

 6's, sometimes hardly distinguishable (figs. 30, 32, 34). The 

 pairs of the smallest group are unequal in size, though frequently 



