1920] Hickernell: Digestive System of Cicada 237 



The tube then becomes closely wound upon itself and as it 

 proceeds forward lies close to the wall of the anterior crop. 

 Signs of functional activity are not as pronounced as the tube 

 is followed forward. The cells contain few or no secretion 

 bodies or vacuoles. Cell particles also cease to be cast into 

 the lumen of the tube. 



The malpighian tubules accompany the ascending intestine 

 forward contributing a large percentage of the mass of the 

 "internal gland." Their walls become extremely thin while 

 the lumen of each vessel increases greatly in size. These 

 ■conditions are represented in Figs. 7 and 9 mt. 



The Descending Intestine. 



While the ascending intestine emerges from the internal 

 ^land its epithelium becomes markedly changed. The cells 

 are low and flat and contain no cytoplasmic inclusions. As 

 the tube leads posteriorly the epithelial lining takes a transi- 

 tional form. This point marks the entrance of the malpighian 

 vessels and the junction of the two intestinal divisions. 



The descending intestine is lined with a single layer of large 

 epithelial cells. Anteriorly these cells are vacuolated (Fig. 18), 

 but in the middle and posterior parts the cytoplasm is uniformly 

 granular (Fig. 19). The lumen of the tube is irregular in out- 

 line by reason of the triangular shape of the limiting cells. 

 These cells are bordered by a zone of cytoplasm much denser 

 than that found centrally. This dense peripheral zone is 

 distinguishable in the basal parts of the cells next to the under- 

 lying muscles as well as at their free borders. This condition 

 reminds one strongly of the ectoplasmic and endoplasmic 

 zones in protozoa. 



The nuclei of these cells are large and centrally placed and 

 contain many coarse chromatic granules. Nucleoli do not 

 appear nor are the nuclei vacuolated as was the case in the 

 ascending intestine. The cytoplasm surrounding the nucleus 

 is finely granular or fibrillar, except in the region immediately 

 following the emergence from the internal gland (Fig. 18). 

 Here both cytoplasm and nucleus may show vacuoles. It is 

 to be noted that here also the vacuolation is not accompanied 

 by the modification of the outer zone of protoplasm as previously 

 ■described. 



