512 E. N. PAVLOVSKY AND E. J. ZARIN 



This hairy lay or of protoplasm stains with iron haomatoxylin 

 in a groy colour, whereas the protoplasm remains black. The 

 hairy band is covered above by a cuticle (not chitinous) ; 

 together with the latter it is cast off into the cavity of the 

 stomach in the form of a peritrophic layer (PI. 16, figs. 6,1, p; 

 figs. 9, 10, p). This casting off is repeated many times, on 

 account of which in the stomach the membranes are disposed 

 in concentrical layers, sometimes in very great numbers 

 (PL 16, fig. 6, p). 



The peritrophic membrane presents a structure known for 

 a long time in the articulated animals. With regard to the 

 bee Petersen has demonstrated that the said membrane of 

 this insect contains a proteolytic ferment. The significance 

 of the peritrophic membrane is interpreted in different ways. 

 Some investigators believe it to serve for the defence of the 

 tender stomach epithelium against mechanical injury by 

 vegetable food, especially by the flower pollen in the bee. 



Such an interpretation cannot be extended to all Arthropods, 

 since an analogous formation is also present in blood-sucking 

 forms (Culex, Anopheles, according to Schaudinn), the liquid 

 food of which cannot do any harm to the walls of the stomach. 

 Probably those investigators are right who regard the peri- 

 trophic membrane as a cuticle formed by the secretion of the 

 stomach epithelium. Originating by transformation of the 

 surface protoplasm of the cells, the membrane itself presents 

 a hard secretion. In the depth of the hairy layer, as in a sponge 

 (PI. 16, fig. 9, jo),is retained the liquid secretion of the stomach, 

 on account of which the same quantity of ferment is capable of 

 acting for a longer period upon the food contained in the cavity 

 of the mid-gut. On account of the relative shortness of the 

 intestine this mode of action of the ferments is of special 

 significance, especially in herbivorous insects, since the food 

 does not pass through the intestine so rapidly, being detained 

 in the folds soaked with the digestive juices of the peritrophic 

 membranes. Thus, in our opinion, they compensate the 

 relatively small length of the intestine in insects. 



(b) At the bottom of the folds of the stomach epithelium 



