398 ELDON W. SANFORD 
in the same way. It cannot be definitely stated whether the fat 
gets merely into the end cells or also into the first of the peri- 
tracheal cells, for cell walls are indistinguishable. I do not 
believe that fat ever gets from the cytoplasm of the tracheal 
cells into the lumen of any tracheae. 
The fat globules found in the peritracheal cells are easily ex- 
plained. They only appear occasionally in my slides, for the 
eytoplasmic layer is very thin in the American cockroach (fig. 
14), and not of such thickness as in the oriental cockroach. The 
peritracheal cells are bathed by the blood which fills the body 
cavity, and they take from the blood the food products which 
they need. The blood contains much fatty substance after fat 
has been eaten, and this substance may readily be absorbed by 
the peritracheal cells and reorganized to fat, which appears in 
globules in the cytoplasm. Similar globules may also be seen in 
the cells of the Malphigian tubules, which are similarly bathed 
by the blood. 
The last phenomenon described by Petrunkevitch is the pres- 
ence of chyme and leucocytes in the tubes. I have found such 
chyme present in practically all my preparations of the crop, and 
leucocytes were often present in it (fig. 14). It was present 
even in the most careful controls, where the animals were im- 
mersed in the green solution before dissection; it usually appeared 
in some of the smaller tracheae, but sometimes in the larger ones. 
There is no doubt that the presence of a sticky deposit is a 
common occurrence in some tracheae of American cockroaches. 
Its origin is very difficult to explain. In view of experiments al- 
ready described, it is certain that it does not enter the tubes 
through the tracheal end cells. My explanation is only tenta- 
tive and cannot be tested experimentally nor verified by obser- 
vation. It is well known that many Orthoptera have difficulty 
in moulting, often dying or sustaining injuries in the process. 
It seems possible that during the moulting of cockroaches slight 
disturbances might cause rips or breaks in the tracheae. This 
would be fatal if it occurred much in the larger tracheae, but 
might cause little inconvenience if it happened in the smaller 
branches. Blood would then fill the torn branches with its con- 
