210 WM. REES B. ROBERTSON 



ary plane according as the one or the other happens to predom- 

 inate. During these changes of form the chromosomes are under- 

 going rapid condensation (fig. 155). As they reach the metaphase 

 stage, we at first get conditions such as are seen in figures 157 

 and 158. 



Figure 157 is a nearly polar view of an early metaphase. The 

 no. 11 chromosome is similar to 156d; no. 10, to figure 156c, 

 except that it must have had very much longer arms than the 

 latter; no. 9, to no. 9 of figure 155a; and nos. 6, 7, and 8, to nos. 

 7 and 8 of figure 155 and to 156c. Whereas no. 6 in figure 155 

 is a ring, it apparently is not so in figure 157; but in Syrbula 

 admirabilis it has been shown (Robertson, '08) that chromo- 

 somes which usually form rings do not always do so. No. 5 is 

 a ring similar to no. 5 in figure 155, while nos. 1, 2, and 3 are 

 rods similar to the corresponding numbers in figures 155 and to 

 figures 156a and 156b. 



Figure 158 is a lateral view with all chromosomes shown. 

 No. 11 is a ring in side view; nos. 1 avnd 2 are rod-like; no. 4, a 

 cross approaching a rod; and nos. 3 and 8, rings. All others 

 are crosses. The sex chromosome is a rod. In the second 

 spermatocytes (figs. 159, 160) there are two sorts of cells, de- 

 pending upon the presence or absence of the sex chromosome. 

 The size relations and rod-like character of the chromosomes 

 can readily be made out here. 



I have given a detailed description of Syrbula to prepare 

 for a better understanding of the chromosomes in 



2. Chorthippus (Stenobothrus) curtipennis Scudd. Chorthippus 

 is unique among Acrididae in having apparently seventeen chro- 

 mosomes. Three pairs of the chromosomes are V-shaped, each 

 with arms of unequal length. This suggests possible com- 

 pounding in chromosomes. These V's have the apices turned 

 toward the center of the metaphase plate. At the apex is a 

 thin place, seemingly a point of union, over which the deepl}'' 

 staining material is not continuous. If we assume that each 

 of the six unusual V's embraces two chromosomes, the number 

 seventeen is increased to twenty-three. If this assumption 

 be correct, the chromosomes may be numbered according to 



