1920] Hickernell: Digestive System of Cicada 231 



intestine through which it goes anteriorly until it reaches the 

 internal gland. After traversing the latter it again starts in a 

 posterior direction through the descending intestine and 

 finally enters the rectum, the last organ of the system. There 

 seems to be no possibility that the food material takes any 

 other course than that outlined above. There are no con- 

 nections between the parts described which would permit any 

 other course, and the presence of valves shows that the food 

 stream could follow only the direction outlined. 



HISTOLOGICAL STRUCTURE OF THE DIGESTIVE ORGANS. 



The Esophagus. 



The epithelium of the esophagus has no prominent cell 

 boundaries. Here and there can be seen cells whose free 

 margins are separated by walls, but for the most part the 

 epithelial lining appears as a syncytium. The nuclei are 

 prominent, being large and containing numerous chromatic 

 granules rather evenly scattered. The nuclei do not all lie 

 near the proximal ends of the cells, but appear near the distal 

 border as well. 



The cytoplasmic portion shows no differentiation between 

 basal and free ends, but is uniformly made up of fine granules 

 or minute fibrillae which seem to compose the more solid portion 

 of the cytoplasmic mass. Here and there are found vacuolar 

 spaces within the cytoplasm, but in no place does one find 

 cytoplasmic inclusions which could be considered as evidence 

 of secretion or absorption. The latter statement is based upon 

 observations upon sections from numerous insects of different 

 ages in which a wide variation as to activity in feeding was 

 possible. The free margin of the epithelium is bounded by 

 a definite wall, but there does not appear to be any cuticula or 

 striated border. The epithelium lining the esophagus would 

 seem, from these observations, to have a purely passive function, 

 conducting the food material posteriorly, but not contributing 

 otherwise to the digestive or absorptive processes. 



The cells of the esophageal epithelium have a well developed 

 basement membrane. Connective tissue elements thicken 

 this in places (in the middle of the folds, for example) in such 

 a way that the folds seem to have a dense core of darkly staining 

 material in which the details of structure do not show them- 



