JOUENALi OF ENTOMOLOGY AND ZOOLOGY 91 



Hum. The fluid is secreted by large glandular cells (G 1) of which 

 four are shown in this section. The fluid is stored up in the reser- 

 voir, which is held in position by two sets of muscles (M^ and M^). 

 Of muscles M\ there are two pairs to each tubercle, one pair being 

 at about right angles to the plane of the other pair. Of muscle M^ 

 there is probably only a single fibre [there is an indication that there 

 is another muscle fibre of M" at the base of the reservoir, but having 

 failed to trace direct connections in the sections, I am not sure 

 whether it exists]. In this figure, both M^ and M" are contracted. 

 M^ holds the upper portion of the reservoir [Ep R] contracted 

 within the tubercle. The blood coming in between the hypodermis 

 of the tubercle (H p) and the epithelium of the reservoir (Ep R) 

 at Sp., forces up the portion of the epithelium of the reservoir 

 immediately below the attachment of muscle M\ as at Ep^ R. At 

 this point the walls of the reservoir are thus partially approximated 

 and form a simple means for closing the mouth of the reservoir, 

 thus preventing unnecessary loss of the secretion by evaporation 

 when the gland is at rest. The lower portion of the reservoir is 

 held in place by muscle M" and in shape by the fluid inside. On the 

 inside of the body the reservoir is bathed by blood and surrounded 

 by a rich supply of tracheae and fat tissues, which are omitted in this 

 diagram. Fig. 2 shows the gland in its eversed position. The 

 gland is pushed out by blood pressure, resulting from a general con- 

 traction of the peripheral body muscles. At the same time, the 

 muscles M^ and M^ relax, the entire reservoir is thus forced for- 

 ward, but only a small portion comes to the outside. Ep R and Ep^ 

 R, which in Fig. 1 are within the tubercle, are here forced to the 

 outside. Further than this point the epithelium cannot be pushed 

 out, it being held back both by M^ and PVP, which have reached the 

 limit of their relaxation. The blood pressure also forces the blood 

 in Sp between Ep R and Ep' R, tending to give to the eversed por- 

 tion of the gland its characteristic globose appearance mentioned 

 above. When this portion of the gland is eversed, a droplet of the 

 fluid contained in the reservoir is forced out and spread on the 

 surface of Ep R and Ep' R, thus providing for a rapid evaporation 

 of the fluid and a quick diffusion of its offensive odor. At the same 



