PHYSIOLOGY OF DIGESTION IN BLATTIDAE 391 
In connection with the question of digestion in insects, a strik- 
ing phenomenon has been described as occurring in the tracheae 
of the alimentary canal. This is the question of the presence of 
fats and other substances in the tracheal tubes after feeding, which 
has been under discussion more or less for about seventy years. 
In 1847 Alessandrini noticed indigo in the tracheal tubes of 
moth larvae after they had eaten food containing indigo, both in 
the tracheal and cells and in the lumen of the tubes. Stimu- 
lated by this finding, Bassi did further work on the same material 
and concluded that Alessandrini’s work was correct, but that 
only certain animals, and often only certain parts of these, 
showed the phenomenon, continuing to show it not only through 
the larval, but also the pupal and adult stages. 
Blanchard injected pigments into the body cavity and found 
them later lying along the inner surfaces of the tracheal walls. 
He believed that they were carried there by the blood stream 
and named the process ‘peritracheal circulation.’ His results 
were quite uniform, and he considered the variability of Bassi’s 
results to be due to variation in the amount of stained food 
previously eaten. 
Soon after this Agassiz started his investigations on the prob- 
lem and arrived at the conclusion that there are two sorts of 
tracheae, one respiratory and one circulatory, the two differing 
considerably histologically. These findings have not been 
substantiated by other authors. 
Sadones found that there are, however, two distinct kinds of 
tracheal endings, one in the epithelium and one in the tissue 
below. Petrunkevitch has verified this. 
Faussek described in certain insects tracheal tubes which enter 
the epithelium of the stomach and possess a distinct lumen 
bounded by plasma and normal nuclei, but no chitinous boundary. 
These were stated to end in sacs bounded by one or two nuclei. 
The appearances of sacs have since been criticized, and I agree 
with the critics that the sacs were probably artifacts caused by 
diffusion or currents. Free ending of tracheae were also de- 
seribed. This is in disagreement with the ideas of most investi- 
gators except Vieweger. The latter has described free intracel- 
