1910] Alimentary Canal of Psychoda Alter nata 301 



ready to molt, were examined and the same identical condi- 

 tions found, the theory of stored up secretions was discarded. 

 This condition of degeneration of the mid-intestinal epithelium 

 has also been found in some specimens collected at random for 

 general structural work, they having been caught in the act 

 of transformation. 



A later stage shows these epithelial cells becoming more 

 broken up by large vacuoles. The entire distal portion of the 

 cells becomes vacuolate with strands of cytoplasm surrounding 

 the vacuoles (Fig. 49). The vacuoles at first circular in sec- 

 tion become irregular in shape as their size increases, while 

 the nuclei are found moving out into the distal more vacuolate 

 portion of the epithelium. All signs of cell boundaries are lost 

 and the epithelium resembles a mass of ragged cytoplasm with 

 nuclei scattered about through it. In the cytoplasm small 

 round concretions are usually present in great abundance, es- 

 pecially in the more vacuolate portion (Figs. 48 and 49, con.) 

 Gregarine parasites are seldom found within the epithelium. 

 The nuclei degenerate unevenly. Some near the basement 

 membrane may retain a more healthy appearance with chroma- 

 tine granules and large nucleolus, while those beginning to mi- 

 grate lose their chromatin. At this stage of degeneration, there 

 appears in the lumen of the mid-intestine, surrounding the peri- 

 trophic membrane and enveloped food contents, a great mass 

 of finely granular and deeply staining secretion which is evident- 

 ly the product of the degenerating cells of the epithelium. 

 This deposit seems to be confined largely to the posterior half 

 of the mid-intestine where the epithelium consists of the tall 

 slender cells. In this bluish-staining deposit are to be seen 

 scattered remains of degenerating nuclei, especially nucleoli, 

 which seem to be especially resistant. Scattered through this 

 deposit are also to be found deeply staining bodies, probably 

 concretions, and a quantity of uniform yellowish secretions, 

 evidently a product of the degenerating cells. 



This degeneration of the mid-intestinal epithelium begins in 

 the posterior portion where the cells are long and slender and 

 as metamorphosis advances, the process of degeneration may 

 be traced forward to the esophageal valve (Figs. 50 and 51). 

 When the large cells of the anterior half of the mid-intestine 

 have become strongly vacuolate, those of the posterior part 

 have almost completely broken down and their contents cast 



