288 Annals Entomological Society of America [Vol. Ill, 



These lar^c eells grade off posteriorly into a region of tall 

 slender seeretory cells (Fig. 2, cp.), comprising the posterior 

 third of the mid-intestinal epithelium. These slender cells are 

 finely vacuolate and have a very strongly developed striate 

 border (Fig. 24, st. b.) The nuclei are small, usually centrally 

 located, with deeply staining nucleoli and chromatin material. 

 During active secretion, groups of these cells increase greatly in 

 heighth and protrude into the lumen, giving to the inner margin 

 of the epithelium a decidedly uneven surface (Fig. 23. cp.) 

 In this respect, this region stands out in sharp contrast with the 

 anterior region of large cells, where their inner margins form 

 almost a straight line. Here and there among these slender 

 cells as well as the larger anterior ones are to be found huge, 

 coarsely vacuolate cells which protrude into the lumen. These 

 have been described as mucus celts (Fig. 46, m. c.) 



The striate border is more or less developed throughout the 

 whole length of the secretory part of the mid-intestine, but its 

 greatest development is to be found in the posterior region 

 during active secretion and just before molting. Some of the 

 earlier workers considered the striate border as a chitinous inti- 

 ma perforated by many fine canals. Later work goes to show, 

 however, that it is simply a ciliate border, consisting of non- 

 vibratile cilia, except perhaps in case of Chironomus larvae 

 (Vignon '99). In Psychoda alternata it grades gradually from 

 the vaculate tips of the cells into a clear homogenous border 

 formed by closely appressed fine cilia. So gradual is the grada- 

 tion and so intimate is the relation between the cell body and 

 the border that I am inclined to agree with Van Gehuchten 

 ('90) that the cilia are continuations of the cells rather than 

 secretions deposited by them upon their inner margin. 



The basement membrane is quite distinct throughout the 

 whole length of the mid-intestine (Figs. 22 and 24. b. m.) 

 In places it is considerably thickened. With perfect fixation 

 the basement membrane remains closely connected with the 

 epithelium. It bears on its outer surface, or more often in 

 slight depressions of it, the numerous strands of circular muscles. 



In the region of the eso[)hageal valve, and for a short dis- 

 tance caudad, the circular muscles are weak and the strands far 

 apart (Fig. 20, c. m.) But beginning with the region of very 

 large epithelial cells and extending back along it a short distance 

 the bands of circular muscles become much broader and more 



