THE MECHANISM OF SECRETION 



327 



for excretion ; then the cellular membrane swells out, and a part of 

 the protoplasmic body projects into the intestinal cavity. 



Before going farther, the terms secretion and excretion should, he 

 says, be defined. With Ranvier, he believes that the elaboration in 

 the protoplasm of a definite fluid substance is, par excellence, the 

 secretory act, while the removal of this substance is the act of 

 excretion. 



A glandular cell of the chylific stomach, when at rest, is always 

 furnished with a striated " platform," or flat surface, or face, on the 

 side facing the cavity of the stomach, and the free edge of the plat- 

 form, or plateau, is provided with filaments projecting into the 

 digestive cavity (Fig. 322, /). These glandular cells, when active, 



A 



FIG. 322. Different phases of the mechanism of secretion and of excretion. After Gehuchten. 



differ much in appearance. In a great number, the platform (pla- 

 teau) has disappeared, and is replaced by a simple, regular mem- 

 brane. During the process of secretion, a finely granular mass, in 

 direct continuity with the protoplasm, swells, and raises the mem- 

 brane over the entire breadth of the cell, causing it to project into 

 the intestinal cavity (Fig. 322, A, B). These vesicles, or drops of 

 the secretion, whether free or still attached by a web to the cells, 

 are clear and transparent in the living insect, but granular in the 

 portions of the digestive canal fixed for cutting into sections. Ge- 

 huchten then asks : " How does a cell gorged with the products of 

 secretion empty itself?" Both Ranvier and also Heidenhain be- 

 lieve that one and the same glandular cell may secrete and excrete 

 several times without undergoing destruction, but their researches 



