328 TEXT-BOOK OF ENTOMOLOGY 





 made on salivary glands have not answered the question. Gehuchten 



explains the process thus : when the epithelial cell begins to secrete, 

 the clear fluid elaborated in the protoplasm of the cell increases the 

 intra-cellular tension, until, finally, the fluid breaks through certain 

 weak places in the swollen basal membrane of the platform, and 

 then easily passes through the closely crowded filaments, and pro- 

 jects out into the intestinal cavity as a pear-shaped vesicle of a 

 liquid rich in albumens at first attached to the free face of the cell, 

 but finally becoming free, as at Fig. 322, A, B. 



When the elaboration of the substance to be secreted is more 

 active, the mechanism of the secretion is modified. The basal mem- 

 brane of the platform may then be raised at several places at once ; 

 instead of a single vesicle projecting into the intestinal cavity, each 

 cell may present a great number more or less voluminous. If all 

 remain small and rapidly detach themselves from the glandular cell, 

 the filaments of the platform are simply separated from each other 

 at different points of the free face, as in Fig. 322, C. On the other 

 hand, when the different vesicles of a single cell become larger, the 

 filaments of the platform are compressed and crowded against each 

 other in the spaces between the vesicles remaining free, and the 

 undisturbed portions of the platform appear homogeneous (Fig. 

 322, Z>). After the excretion of the secretory products by this 

 process of strangulation, the cell then assumes the aspect of a glan- 

 dular cell at rest, and may begin again to form a new secretion. 



To sum up : The process of excretion may occur in two ways : 

 1. Where the membrane ruptures and the substances secreted are 

 sent directly out into the digestive cavity. 2. Where the vesicles 

 become free by strangulation, floating in the glandular or intestinal 

 cavity, and ending by rupturing and coming into contact with the 

 neighboring vesicles or with the food. 



Absorbent cells. Besides the glandular or secreting cells in 

 Ptychoptera, there is between the two regions of the chyle-stomach 

 lined with these cells a region about a centimetre long composed of 

 absorbent cells. The absorbent cells are very large, polygonal, and 

 contain a large nucleus, in which is a striated convoluted chromatic 

 cord. 



The food on entering the chyle-stomach is brought into contact 

 with the products secreted in the proventriculus, in the first part of 

 the chyle-stomach, and in the tubular glands. These products of 

 secretion act on the food, extracting from them useful substances 

 which they render soluble. These substances, after having been 

 absorbed by the absorbent cells in the middle region of the stomach. 



