238 Annals Entomological Society of America [Vol. XIII, 



A comparison of sections of the ascending and descending 

 intestine shows that their color is due to the histological structure 

 of the cytoplasm in each case, the yellow color of the former 

 being caused by the numerous inclusions. The complete 

 absence of these in the descending intestine results in a color 

 difference which enables one to recognize this tube with the 

 naked eye. 



The Rectum. 



The rectum is relatively short and its diameter is much 

 greater than that of any part discussed thus far except the 

 posterior crop. Its walls are also much thicker than those of 

 any other part of the digestive tube. The epithelial lining is 

 similar to the esophageal epithelium in that the columnar cells 

 are narrow, closely packed, thrown into numerous small folds, 

 and the cell boundaries are indistinct. The muscle layers do not 

 have their fibres running in strict longitudinal and transverse 

 directions, but there are many strands of muscle material 

 running in criss-cross fashion so that a sort of woven mat of 

 tissues makes up the muscular part of the rectal walls. In 

 places, however, distinct layers may be seen, an inner thin 

 longitudinal layer and an outer thick circular layer. The 

 muscle is of the striated variety in both layers and is gathered 

 into typical bundles. The great thickening of the circular 

 layer is not surprising in view of the functional activity of this 

 layer in emptying the rectal cavity. 



V. Relative Conditions in Male and Female. 



The different divisions of the digestive tube in the female 

 adult do not differ greatly from those described in detail for 

 the male. The gross and microscopic arrangement of parts 

 is the same in general plan. Esophagus and anterior crop are 

 practically identical in structure in the two sexes. The posterior 

 crop is much smaller in diameter in the female, its walls being 

 crowded together by the surrounding fat and reproductive 

 organs, but the walls themselves are similar in structure to 

 those of the male. Ascending and descending intestine and 

 rectum show no structural differences in the two sexes. There 

 is, then, no great difference in the general plan and arrangement 

 of the digestive organs of the male and female. 



