768 Wisconsin Academy of Sciences, Arts, and Letters. 
to end; at its anterior end each fold has a narrow beginning 
and is fairly straight for a distance of lmm, it then widens, 
becomes irregular and shows a great many indentations and 
transverse folds. The ileum at its posterior end becomes nar¬ 
row and here the folds end. An examination of the entire 
surface shows that there are six of these apparent folds. 
A study of transverse sections through this region shows 
that these apparent folds are in reality due to an equal num¬ 
ber of internal folds. Where each internal fold sinks in from 
the wall it makes, on the external surface, a distinct, irregular 
furrow; these furrows appear dark from an external view and 
give the appearance of external folding to the regions be¬ 
tween them. The relation of the apparent external and real 
internal folding is best understood hv a comparison of the sur¬ 
face view of the ileum (fig. 26) with a section through the 
same region (fig. 28). 
Faussek (10) found in the nymph of Aeschna that in the 
hind-intestine there were two different kinds of cells. He says: 
“Die ganze oberfiache des Diinndarmes namlich ist mit einem 
Epithel bedeckt, das nicht, wie gewohnlich, gleichartig ist, 
sondern zwei, der Grbsse und deni Charakter seiner Zellen nach r 
scharf sich unterscheidende Formen zeigt. In der Vertheilung 
derselben is gar keine Regelmassigkeit zu bemerken; sie sind 
Stellenweise auf der Wand cles Diinndarmes zerstreut, und 
wechseln mit einander ab”. He then speaks of the large cells 
with the large nuclei in contrast to the smaller ones. While 
this description from Faussek is in part true here there are 
some difference between the Aeschna nymph and the imago 
of Libellula Jrmaculata. In the latter the large cells are en¬ 
tirely restricted to the ileum and confined there to three places. 
When one examines the ileum after it has been cut open, stained 
and mounted with the inner surface uppermost, the three 
areas to which the large cells are confined can be distinguished 
by the size of the cells and of their nuclei. It is seen that 
there is a large area of these cells near the anterior end of the- 
ileum and two small areas lying near the posterior end. 
