1920] Hickernell: Digestive System of Cicada 235 



The opening from posterior crop into the ascending intestine 

 is surrounded by a sort of transitional epithelium. Here the 

 cells are tall and closely packed. They are thrown into slight 

 folds (Fig. 14) but not to the extent found in some other portions 

 of the digestive epithelium. There is a well-developed layer of 

 circular muscles at the place where the tube arises, presumably 

 a sphincter or valve, guarding the opening into the ascending 

 intestine. 



The Ascending Intestine. 



The ascending intestine, in histological structure, shows 

 great difference from the parts previously described. The 

 lining of this tube is composed of a single layer of irregular 

 epithelial cells which, when fully developed, are very large 

 (Figs. 15 and 16) and have a prominent, centrally-located 

 nucleus. Of all the digestive epithelia thus far considered, that 

 of the ascending intestine seems to be most active. The 

 cytoplasm at the base of each cell is granular, but as the free 

 end of the cell is approached large globules are developed 

 (Fig. 16). When the globules are not present, vacuoles of 

 varying sizes are found in the protoplasm near the distal ends 

 of the cells (Fig. 15). 



The nuclei of the large fully-developed epithelial cells 

 become vacuolated just previous to secretion. At the bases 

 of the larger cells are found numerous small replacement 

 nuclei which suggest the method by which new cells are formed 

 to- take the place of those cast off. In Fig. 17 the lighter 

 colored cells are apparently in process of developing to replace 

 those destroyed by secretory activity, while the darker ones 

 are about to secrete. The free margin of the cells is bounded 

 by a well-developed striated border. This is so prominent 

 that at certain times it gives the cells the appearance of being 

 clothed with short cilia. 



The epithelial cells lining the entire tube from its place 

 of origin to the point where it goes into the internal gland 

 show signs of functional activity of the sort above mentioned. 

 Figs. 15, 16 and 17 represent different phases of the secretory 

 process. 



At the base of the epithelial layer is a thin stratum of 

 circular muscle fibres. In some places this is hard to dis- 

 tinguish from the basement membrane of the epithelial cells. 



