120 N. E. MCINDOO 



cells in the dorsal and ventral portions of this antenna did not lie 

 in the same plane. It is to be noted that only about one half of 

 each group of sense cells lies in the indentation of the chitin, and 

 that each group is surrounded by a neurilemma (Neu), which, 

 at places, unites with the hypodermis. At this place in the 

 antenna the nerve is always divided into several branches (NB), 

 and in longitudinal sections these branches may be traced to the 

 groups of sense cells. 



2. External structure 



The superficial appearances of the two types of olfactory 

 organs observed under a low-power lens have already been 

 mentioned, and now these appearances observed under a high 

 power lens will be describedi 



a. Single olfactory organs. Viewed externally under a high 

 power lens, each olfactory pore is always surrounded by a pore 

 border (fig. IG, PorB), which is usually slightly darker than the^ 

 surrounding chitm, although occasionally it may be considerably 

 darker (fig. 21). The degree of darkness of the borders seems 

 to depend on the development of the yellowish formations around 

 the cones and pore cavities of these organs. The hair sockets 

 are also surrounded by borders, which are generally darker 

 (figs. 17, 21 and 22) than the surrounding chitin, but on certain 

 parts of the integumen' they may be considerably lighter in color 

 (fig. 19). As a rule, the pore borders are striated, but the borders 

 around the hair sockets never show striae. The striae are radi- 

 ally arranged, running from the pore wall to the periphery of the 

 border (figs. 16 to 25). This is the first time that the writer has 

 ever observed striae in the borders of olfactory pores. 



The inner margin of the border is bounded by a darker line, the 

 pore wall (fig. 16, PorW), which may be circular or oblong in 

 shape. Generally speaking, the width of the pore border, the 

 diameter of the pore aperture, and the size of the sense cell are 

 directly proportional to the diameter of the pore wall. This 

 means that the size of these organs, which varies considerably, 

 is determined by the diameter of the pore wall. The chitin 



