1957 ] Parsons — Esophageal Valve in Hemiptera 145 
Although the increasing complexity of the valve, from 
Notonecta and Ranatra to the corixids, represents a mor- 
phological sequence, I, like Marks, will not here attempt to 
draw any phylogenetic conclusions. In terrestrial Heterop- 
tera, both simple and complex esophageal valves are rep- 
resented ; in Oncopeltus fasciatus, the valve resembles that 
of Notonecta (Hood, 1937), while the esophageal invagin- 
ation of the cacao capsid bug (Goodchild, 1952) is similar 
to that of corixids. 
4. Sutton’s Interpretation of the Significance of the Cor- 
ixid Esophageal Valve 
Sutton proposed that the complex valve of corixids is a 
primitive feature. This theory was based primarily on her 
belief that the primitive corixids secreted two kinds of 
peritrophic membranes, one from the cells of the posterior 
midgut (the Type I of Wigglesworth, 1950) and a second 
from the anteriormost midgut cells of the perivalvular re- 
gion (Wigglesworth’s Type II). Sutton’s hypothesis was 
that modern corixids have lost the second type of mem- 
brane, but have retained the first type. The latter theory 
is to be the subject of another paper (Parsons, in press) ; 
the proposal that corixids once secreted a Type II mem- 
brane will be discussed here, however, since part of Sutton’s 
evidence for this hypothesis is based upon an apparently 
incorrect interpretation of the nature of the annular cells. 
When the ancestral corixid secreted a Type II peritrophic 
membrane, according to Sutton, a long esophageal invagin- 
ation was present ; this helped to mould the membrane and 
to move it posteriorly by alternate extension and retraction. 
The membrane was secreted by the anterior cells of the 
perivalvular region. In the course of evolution, the latter 
region has lost its ability to secrete chitin, but it has not 
yet acquired a digestive function. If any food were to get 
into this non-functional region, it would only decompose; 
to prevent this, Sutton claimed, the long esophageal invag- 
ination has been retained in modern corixids. 
Sutton cited the work of Aubertot (1934), who, in his 
study of the peritrophic membrane in many orders of 
insects, distinguished a groove or “sillon” which marks the 
