270 KANSAS UNIVERSITY SCIENCE BULLETIN. 



the name of salivary injector. The reasons for the choice will 

 appear as the discussion proceeds. 



From sections we learn that the injector is a chitinized cylin- 

 der, furnished with a plunger, inlet and outlet tubes, and 

 Valves. An idea of its structure may be obtained from figure 

 14. One of the retractor muscles (fig. 14, m.in) is shown, 

 although, correctly, it should not be figured in a median longi- 

 tudinal section. The cylinder is conical at the cephalic end, 

 compressed in the middle, and invaginated at the back. The 

 central portion of the invagination is strongly chitinized, and 

 serves as the point of attachment for a tendon which divides 

 and sends a part to each of the large muscles of the injector 

 (fig. 3, m.in). The rim of the cylinder is connected with the 

 invaginated part by strong, elastic chitin. The normal posi- 

 tion of the injector is that given in figure 14. 



Among the Heteroptera Geise noticed, in regard to shape, 

 two types of the injector. The water forms were all slightly 

 spherical, while the land forms were cylindrical. A suggestion 

 offered by him to account for the difference is, that the latter form 

 gives greater elasticity, which might be required by the land 

 form in forcing saliva into woody tissue. If this be true, we 

 should expect to find the cylindrical form among the cicadas, 

 and such is the case. 



In the ventral side of the cylinder the entrance for a duct may 

 be found. A valve (fig. 14, v) guards the opening, with the 

 tip of its flap pointing toward the cephalic end of the cylinder. 

 From this entranceway a single duct leads backward. As it 

 leaves the encircling hypopharynx it divides, and in the caudal 

 view (fig. 3, sd) these divisions may be easily traced. They 

 lead back to the glands which fill the rear and upper part of the 

 head chamber. 



The cephalic portion of the cylinder narrows into a dark, 

 heavily chitinized tube with which the hypopharynx is fused. 

 Shortly beyond the point where the hypopharynx fuses, the 

 tube coalesces with the pharyngeal canal, and the two pass for- 

 ward as the tongue-shaped structure already mentioned in the 

 discussion of the hypopharynx. The true nature of the struc- 

 ture may now be understood. It is the organ referred to by 

 Savigny as ligula or hypopharynx. It is formed, first, by a 

 fusion of the hypopharynx with the outlet of the injector ; and. 



