114 Wisconsin Academy of Sciences, Arts, and Letters. 
portion thus extending into the mid-intestine as a double fold 
has the same character of epithelium as the fore-gut, and further 
proof of its origin is given by the layer of chitin extending to 
the point where the folded portion meets the anterior end of 
the mid-intestine. The length of this part is about one-half 
the width of the anterior end of the intestine,, so that if pushed 
forward by the food it might nearly, if not quite, close the open¬ 
ing. An oesophageal valve is thus formed. (Fig. 3.) As the 
posterior portion of the oesophagus as well as the intestine is 
usually distended with food, the chitinous hooks of the oesopha¬ 
gus probably aid in the function performed by the valve. 
At the beginning of the mid-intestine there is a marked change 
in the epithelial cells, which are here columnar and bear on 
their inner surfaces a well-marked peritropliic membrane, the 
thickness of which is about equal to the average width of the 
cells. (Fig. 5.) Nests of regenerative cells, very similar in ap¬ 
pearance and staining reaction to those described by Needham 
(7) for certain dragon-fly nymphs, are numerous, and placed 
at regular intervals. A thick basement membrane and longitud¬ 
inal muscle fibers are present, the latter somew'hat scattered. 
The circular fibers form a nearly continuous coat and are un- 
striated. 
This columnar epithelium extends to a point a little posterior 
to the openings of the Malpighian tubules, but the peritrophic 
membrane is supplanted by a chitinous layer just at the poster¬ 
ior border of the lumen of the tubules. That is, the beginning of 
the hind-intestine is marked only by the change from peritrophic 
membrane to chitin, and not by an immediate change in the 
character of the epithelium, except that no nidi are present pos¬ 
terior to the tubules. (Fig. 4.) Within a short distance, how¬ 
ever, the columnar epithelium gives way suddenly to a layer 
of flattened epithelial cells similar to those of the oesophagus. 
The chitin covering this area of columnar epithelium of the 
hind-intestine, is beset with numerous spines. At about the 
middle of the small intestine another band of chitinous spines 
is developed and a heavy band of circular muscles is present 
just at this point, indicating that the structure probably acts 
as a rectal valve. (Fig. 6.) 
