110 W. R. B. ROBERTSON 
The sex chromosome—single in the male and paired in the 
female—may rank in size as No. 5 (Tettigidea), No. 3 (Paratettix) 
or No. 1 (Acridium), depending upon the genus, but this variation 
between different genera does not seem to be accompanied by 
any very considerable difference in the relative sizes of the ordi- 
nary chromosomes. 
Of the constancy of these size relations, I am very certain, 
having examined a large number of individuals in each species. 
Being certain of the size relations, I was very ready to recognize 
any abnormal variations in this respect when they appeared. I 
found such variations in two genera: two cases in Tettigidea 
parvipennis, only one of which is given (figs. 4-8), and two in 
Acridium granulatus (figs. 11-13). 
1. A DEFICIENT NO. 4 CHROMOSOME IN TETTIGIDEA 
PARVIPENNIS 
To understand the abnormal chromosomes we must first 
examine the normal ones. Figures 1 to 3 are of cells from 
normal individuals. Figure 1 is from the wall of an egg tube. 
It shows 14 chromosomes, the number characteristic of the fe- 
male. The chromosomes are numbered and paired according 
to size. Two of the chromosomes (nos. 1 and 2) have been 
drawn at one side for convenience. This figure is also typical 
for male 2 x cells, with this exception, that the sex-chromosome, 
No. 5, is always unpaired in the male. Figures 2 and 3 are 
lateral views of the first maturation division in the male germ 
cells. These show the members of pairs about to separate from 
each other. The members are still in contact at the distal ends 
in most cases. The No. 7 pair in figure 2 has formed a cross and 
is still paired through a greater extent than in the other pairs. 
The sex chromosome ranks fifth in size in Tettigidea and may be 
seen passing undivided to one pole in these cells. Among the 
autosomes (ordinary chromosomes) of figures 2 and 3 there can 
be seen a very slight difference in size between the 1’s and 2’s, 
a considerable difference between the 3’s and 4’s, and a much 
greater difference between the 6’s and 7’s. We are concerned 
at present with the relative sizes of the 3’s and 4’s only. 
