302 Annals Entomological Society of America [Vol. Ill, 



into the lumen. The method, by which the midintestinal 

 epithelium, in this form, is cast off, in no wise reseml)les that 

 described for Hydrophilus, after feeding, where the ei)ithelium 

 with its basal chitinous layer is cast off bodily; nor is it so com- 

 plete and regular as that described by Mobiisz for Anthrenus. 

 It more nearly resembles the degeneration of the mid-intestinal 

 epithelium of dragonfly nymphs after feeding. The individual 

 cells themselves break down and are sloughed off rather than 

 the epithelium in mass being cast into the lumen. 



The extent to which this degeneration takes place is not 

 always easy to determine. It can be followed to where practi- 

 cally all of the old nuclei have migrated out into the lumen and 

 degenerated (Fig. 51). And where practically all of the cell 

 content is dis.solved, although for a time, at least, a quantity 

 of the cytoplasm remains in contact with the basement mem- 

 brane, which is not cast off. I am inclined to believe that this 

 is as far as the degeneration of the mid-intestinal epithelium 

 proceeds in this form. The old adhering cytoplasm is appar- 

 ently absorbed by the newly developing epithelium. 



Between the epithelium of the mid-intestine and its under- 

 lying basement membrane are to be found numerous very small 

 regenerating cells from which the new epithelium is developed 

 (Figs. 48, 49, 50, 51, r. c.) These small cells are extremely 

 difficult of detection except at the time of transformation. Cell 

 division takes place in these embryonic cells while their diameter 

 is yet scarcely one-fifth that of the nucleus of mature epithe- 

 lial cells, so that it is extermely difficult to make out the type 

 of division, but from a study of my preparations it would seem 

 that here we have direct cell division (Fig. 54). They may be 

 collected in small groups or in pairs or scattered singly along 

 the basement membrane. The first structure that can be defi- 

 litely made out is the deeply staining nucleus, but as the degen- 

 ration of the old epithelium advances, a definite cell form can be 

 distinguished. The cytoplasm at the beginning is a mere border 

 about the nucleus, but as development advances it rapidly 

 increases in bulk and comes to form a distinct cell body about the 

 nucleus. By the time the old epithelium is nearly all sloughed 

 off these new cells have come to i)rotrude up into the adhering 

 cytoplasm of the old cells, which they seem to absorb in part 

 (Fig. 51, r. c.) 



