1910] Alimentary Canal of Psychoda AUernata. 293 



practically all of the cells were destroyed by the process of 

 excretion and a complete new epithelium formed from scattered 

 nidi or regenerating centers. Frenzel ('85), Vangel ('86), 

 Bizzozzero ('93) and Rengel ('97) described even more striking 

 cases of epithelial degeneration and regeneration in adult water 

 beetles of the genera Hydrophilus, Hydrobius, Hydrous and 

 Cybister. These beetles like the nymphs of dragonfiies, feed 

 intermittently, being able to fast for periods when food is not 

 at hand and then when food is abundant, devouring great 

 quantities of it. In these bettles the entire epithelium with its 

 basal chitinous membrane is described as being cast off after 

 each full feeding. The new epithelium is quickly developed 

 from highly specialized regenerating centers or nidi, which pro- 

 trude through the muscular coat of the canal, to form distinct 

 diverticula. 



The merocrine type of secretion is found in the mid-intestinal 

 ■epithelium of those insects which feed continuously and which 

 require a continuous supply of digestive fluids. In these forms 

 the cells are always active, the extent of the secreting activity 

 depending upon the extent of feeding. But since the cells are 

 not destroyed by secretion and excretion there is no occasion 

 for any regeneration in connection with the intake of food and 

 digestion. This type of epithelial secretion was described by 

 Van Gehuchten ('90 and '93) for Ptychoptera contaminata, 

 there being no epithelial regeneration associated with digestion. 

 Folsom and Wells ('06) describe this as the prevailing type of 

 secretion in the mid-intestine of Collembola, there being no 

 regeneration at the time of feeding. 



Psychoda alternata in its larval state is not an intermittent 

 feeder but is most at home at the mouth of open sewers, in 

 cultures of decaying horse manure or other vegetable ferments, 

 where it finds abundance of food always present. An occasional 

 plankton form may be found mingled with the food but the 

 bulk of the intestinal contents consists of bits of decayed 

 vegetation. The larva is a voracious feeder and extremely 

 active, scarcely refraining from feeding long enough to molt. 

 The canal always has a great quantity of food material in it, 

 even at the molting periods. From careful study of the epithe- 

 lium of the mid-intestine of this form, I find the merocrine type 

 of secretion prevailing and an absence of epithelial regeneration 

 associated with feeding. 



