1910] Alimentary Canal of Psychoda Alternata 299 



reappear and the normal epithelium is again restored. Since 

 the forms studied lacked Malpighian vessels, Folsom & Wells 

 concluded that this periodical discharge of half of the epithelium 

 with concretions, inclusions and parasites had an excretory 

 function similar to that of the Malpighian vessels in other 

 insects. The short inactive period preceding each molt made 

 it possible to get any desired stage of transformation. Here 

 we find only partial epithelial regeneration at each molting 

 period. 



We shall now consider a more specialized type of insect, 

 one with complete metamorphosis, and see how the changes in 

 the mid-intestinal epithelium at the time of the larval molts 

 compare with those in Collembola at the molting periods. 

 Mobiisz ('97) studied the changes in the mid-intestinal epithe- 

 lium of Anthrenus during the larval molts and found that the 

 same changes appeared then as at pupation, only less intensive. 

 In the study of his preparations, which included larvae in var- 

 ious stages of transformation, he found a large mass of material 

 in the lumen of the mid-intesine which he first mistook for 

 parasites. Further studies revealed to him that this inclusion 

 was simply the remains of the sloughed off epithelium. He was 

 able to find various stages in the throwing off of the old cells 

 from that in which, by muscular contraction and development 

 of the new epithelium, the old with its basement membrane was 

 separated from the muscular coat, to that in which it was cast 

 into the lumen and digested leaving its residue enveloped in the 

 resistant basement membrane. Mobiisz takes exception to 

 Rengel's work on Tenebrio molitor ('96) where he describes 

 the nidi as being cast off with the old epithelium and basement 

 membrane and later making their way through the basement 

 membrane and regaining an attachment to the muscular coat. 

 Rengel must certainly have had faulty preparations. Mobiisz 

 found the nidi retaining their attachment with the muscular 

 coat and concluded that either, the cells of the nidi being 

 embryological, no basement membrane was produced beneath 

 them, or if produced it was dissolved so that it would slip off 

 over them when it was cast off with the old epithelium. By 

 multiplication the cells of the nidi quickly produce the layer of 

 new epithelium. In fact these first changes are produced with 

 such rapidity that Mobiisz failed to catch them in any of his 

 specimens. The new epithelium soon developes its basement 



