PHYSIOLOGY OF DIGESTION IN BLATTIDAE 359 
surface of any single organ, being 2.5 em. in length and on the 
average 0.6 cm. in diameter when distended with food, thus 
having a surface of about 3 sq. em. as against a corresponding 
surface of 0.7 sq. em. in the stomach, which is 1.3 em. in length 
and 0.25 em. in diameter. 
The stomodeum, or that part of the anterior alimentary canal 
which is turned in during the embryonic period, is of considerable 
size in the American cockroach, and may be divided into six 
parts: mouth cavity, pharynx, oesophagus, crop, anterior giz- 
zard, and posterior gizzard. The mouth cavity and pharynx 
were not studied, for it is most improbable that any important 
digestive changes occur there. The salivary glands are paired, 
one lying on each side of the crop along about half its length. 
The ducts run forward into the mouth and are strengthened 
by a tough spiral structure similar to that of the tracheal tubes. 
The reservoir of the salivary secretion may be very large, it 
may be almost as long as the crop when it is dilated with fluid. 
Oesophagus. The oesophagus begins where the dilation of the 
pharynx ends and varies much in size according as it is dilated 
with food or not. When empty its cavity is nearly obliterated 
by closely appressed folds. These folds are continuous with 
those of the crop to such an extent that it is impossible to say 
where one ends and the other begins. The oesophagus wall 
consists of a single layer of nearly cubical epithelial cells (fig. 1), 
between which are seen muscle processes and tracheal end cells 
similar to those described by Petrunkevitch. Within the layer 
of cells and secreted by it is the chitinous intima, of about the 
same thickness as the cells. This is raised into projections, on 
the summits of which long bristle-like processes are situated. 
Around these structures is a layer of circular muscles. 
Crop. The crop is by far the largest part of the alimentary 
canal and no doubt has an important function, though Schliiter 
considers it as a mere storage organ and conducting tube to 
the stomach. The wall consists of three layers, muscular, epi- 
thelial, and chitinous. The muscular layer consists of two 
layers of striated fibers at right angles to each other. One layer 
consists of circular muscles and serves to contract the crop walls 
