1S57 1 Parsons — Peritrophic Membrane in Hemiptera 121 
It is unfortunate that the chitosan test cannot be applied 
to sectioned material. However, Sutton’s technique is open 
to criticism. The corixids, unlike Ranatra, are able to ingest 
particulate food, and histological sections through their 
midguts often show sizeable fragments of exoskeleton from 
small Crustacea and other arthropods within the food mass 
(PL 9, Figs. 2 and 3). The presence of setae or surface 
sculpturing on these fragments indicates that they are of 
foreign origin rather than secretions of the midgut epithe- 
lium. The chitin in these pieces could withstand potassium 
hydroxide treatment as well as could a peritrophic mem- 
brane, and it seems unlikely that the former could be 
distinguished from the latter, using Sutton’s technique. 
To test this hypothesis, the chitosan method was applied 
to the midguts of eighteen Hesperocorixa interrupta, using 
Sutton’s technique. In one of these, a positive result was 
obtained. A small piece of material, approximately 0.5 mm. 
square, withstood the potassium hydroxide treatment and 
reacted positively to the subsequent tests. Examination of 
this fragment under the compound microscope showed it to 
be rolled up like a scroll, its surface covered with small 
hairs. It bore much resemblance to the pieces seen in 
histological sections through the food mass in corixids. 
In the author’s opinion, the chitinous nature of the 
“membranelles” described by Sutton in the midguts of two 
species of corixids has not been sufficiently proven. Some 
test must be devised which can distinguish between secreted 
and ingested chitin before this point can be settled. How- 
ever, the discovery of a peritrophic membrane in Ranatra, 
in which ingested particles have never been observed, 
supports Sutton’s conclusion that this structure is not 
absent in the Hemiptera. It may be, as she has suggested, 
that the Type I membrane is a primitive feature which 
has been inherited from the ancestral hemipteran. It seems 
quite possible that further study will reveal its presence in 
other species of the Hemiptera. 
