546 PROCEEDINGS OF THE ACADEMY OF [Aug., 



Its cytoplasm is less granular. It is always partially, and some- 

 times almost totally, filled with globules {Glo). 



Chiefly on account of its size, a fat cell should never be mistaken 

 for a gland cell. Fat cells are always larger, and sometimes several 

 times larger, than these gland cells. They are found on all sides 

 of the mass of gland cells, but seldom among them. Their structure 

 is similar to that of cenocytes, but the globules are much larger, 

 more conspicuous and are so abundant that the nucleus is scarcely 

 visible. Fig. 7 represents a small fat cell, still alive and stained 

 slightly with a weak solution of methylin green. 



To ascertain if the tubes connecting the gland cells with the chitin 

 are composed of chitin, articular membranes removed from the 

 abdomens of workers were placed a few hours into a saturated solu- 

 tion of caustic potash. When all the adhering tissues had disin- 

 tegrated, the membranes were cleaned with water and a pencil 

 brush. In all cases the tubes were left attached to the membranes. 

 This proves that they are chitinous. To determine how they 

 terminate in the articular membrane, one of the membranes treated 

 ^vith caustic potash was sectioned. The sections show that the 

 canal of the tube opens freely to the exterior (fig. 8, CanTu). 



Judged by the morphology, we may reasonably conclude that the 

 gland cells secrete a volatile substance throughout their cytoplasm. 

 This substance collects in the ampulla which serves as a reservoir, 

 and from the ampulla it passes through the chitinous tube to the 

 exterior where it runs into the canal. The groovelike indentations 

 in the chitin forming the canal may serve two purposes — (1) to give 

 more flexibility to the chitin, and (2) to retain the volatile secretion 

 and help prevent a too rapid evaporation of it. As long as the 

 abdomen is straight, the canal is well protected and the liquid cannot 

 evaporate rapidly, but when the abdomen is considerably ])ent, 

 the entire canal is more or less exposed to the outside air. 



2. Origin of Gland Cells. 



The scent-producing organs of several 15-day-old worker pupte 

 (counting from the time the eggs were laid) were sectioned. At 

 this stage the chitin (fig. 9, Ch) is just beginning to be formed, and 

 the hypoclermis (fig. 9, Hyp) is very thick. The fat cells (fig. 9, 

 FC) are also not yet completely differcmtiated. The hypodermal 

 cells (fig. 9, HyyC) are long and slender. Most of them near the 

 place where the wide and heavy vein (figs. 2, r/, and 9, v) is later 

 formed, break loose from the hypodcrnuil layer and migrate backward 



