142 
Psyche 
[December 
mitotic rate. This is particularly evident in the corixids ; one 
specimen of Sigara ornata showed 181 mitoses in the an- 
nular cell region. Figure B shows a detail of the annular 
cells in this specimen. Mitoses are not nearly as frequent in 
the annular cells of representatives of the other four fami- 
lies, although Table 1 (below) shows that some amount 
of cell division is always present. 
Table 1 
A 
B 
C 
Notonecta undulata 
28 
5 
3 
Ranatra fusca 
17 
3 
8 
Pelocoris femoratus 
21 
4 
6 
Belo stoma flumineum 
24 
11 
14 
Hesperocorixa interrupta 
and Sigara ornata 
36 
28 
181 
Frequency of mitotic figures observed in the annular cell region. Column 
A. number of valves examined; Column B, number of valves showing 
mitoses in annular cell region ; Column C, maximum number of mitoses 
seen in any one valve. 
It is difficult to account for this high mitotic rate in 
corixids. Verson (1897) reported that in the silkworm, 
cell division in this region adds to the cells of the esopha- 
geal valve. However, degenerating cells are rarely observed 
within the esophagus or the esophageal invagination of cor- 
ixids, and there appears to be no real need for such frequent 
cell addition. The location of the annular cells corresponds 
to that of the imaginal disc which regenerates the foregut 
of nymphs after a moult; it may be that the annular cells 
are remnants of this highly active nymphal region, which 
retain their high mitotic rates. 
3. Comparative Aspects 
In his study of the esophageal valves of four species of 
water bugs, Marks described a sequence of increasing com- 
plexity in the following order: Notonecta , Ranatra, Belosto- 
ma, and Hesperocorixa. In general, the present study sup- 
ports this conclusion. 
The valvular action in Notonecta and Ranatra is derived 
from the circular muscle sphincter which, when it contracts, 
draws together the tall annular cells. There is no real 
