92 JOUKNAL OF ENTOMOLOGY AND ZOOLOGY 



time the blood pressure in Sp, which give the eversed portion its 

 characteristic bead-like appearance, also closes the opening of the 

 reservoir by bringing the lips close together, this providing against 

 excessive discharge of the fluid. In this manner the economy, of 

 which Claus speaks, is easily explained. When the gland has been 

 eversed a few seconds, the peripheral muscles of the body relax, the 

 blood pressure is withdrawn, JVr anci M" contract and the gland is 

 brought back to its normal position as in Fig. 1. 



The eversion of the gland primarily by blood pressure explains 

 the bursting of the gland mentioned in one of the preceding para- 

 graphs. It also explains the yellowish appearance of the fluid dis- 

 charged after the bursting, it being now mixed with the blood. 



As seen, the function of M' and M" is to relax when the gland is 

 eversed and to contract when it is withdrawn. This is in direct 

 contradiction to the statement of Claus, who says that "when these 

 (referring to the set of muscles ^1\ which is the only set he flgures) 

 contract, they bring the movable point of insertion to the relatively 

 fixed one in the tubercle, throw open the closed tubercle and force 

 out the anterior portion of the bag-like, dilated part of the reser- 

 voir, from which there comes out a droplet of the secretion." A 

 glance at the relative position ol the apex of muscle PVP when the 

 gland is retracted and eversed, as seen in figures 3-4 and figure 8, 

 will prove the incorrectness of Claus's interpretation of the function 

 of this muscle. Berlese, while figuring M", omits JVP. He also 

 fails to explain the function of this muscle or to state how the 

 eversion and retraction of the gland is accomplished. 



Histological Structure 



The epithelium of the reservoir is an inpocketing of the hypoder- 

 mis, and consequently consists of a layer of cells lined with chitin. 

 The cells are much smaller than the cells of the hypodermis, and are 

 very irregular. (Fig. 12.) They are flattened and broad at the 

 base and more or less pointed towards the chitinous intima. The 

 nucleus is relatively large, occupying the greater part of the cell 

 body, and is coarsely granulated, staining quite deeply. The cyto- 

 plasm, on the other hand, is very finely granulated. Lying close to 



