THE OLFACTORY SENSE OF ORTHOPTERA 421 



maining portions of the integument are semitransparent (repre- 

 sented by lines). 



Many hypodermal gland pores (fig. 89) were observed on the 

 ventral surface of the labrum ; at first sight they may be mistaken 

 for the 4 or 5 olfactory pores found on the dorsal surface of the 

 labrum, but a careful study of them shows that they differ consid- 

 erably in structure. The narrow aperture leads into the spher- 

 ical reservoir, which connects with the gland cell (GIC) ; about 

 one-half of the space in the peripheral end of this cell is occupied 

 by the ampulla, in which the secretion apparently collects, and 

 then this substance runs into the reservoir. The gland cell has 

 only one pole, while the sense cell (fig. 77, SC) has two; and the 

 olfactory organ has neither a reservoir, nor an ampulla. As far 

 as known to the writer, these glands in the labrum of the grass- 

 hopper have never been described before, although the literature 

 pertaining to hypodermal glands has not been consulted. 



THE ANTENNAL ORGANS 



Several investigators have studied the morphology of the an- 

 tennal organs in Orthoptera, but since certain drawings of the 

 acridid Tryxalis nasuta L., by Rohler ('05) best illustrate these 

 organs, the following discussion will be taken only from his work. 



The antenna of either a male or female of the preceding grass- 

 hopper consists of seventeen segments, which bear three types 

 of sense organs as follows: The slender, strongly chitinized 

 bristles are found on the first to eighth segments, but most of 

 them lie on the third segment; the pegs (fig. 90, Pg) lie on 

 all the segments, but most abundantly on the middle seg- 

 ments, and the so-called olfactory organs, pit pegs (PPg), lie 

 on the third to seventeenth segments, but most abundantly 

 on the tenth to fifteenth segments. The total average number 

 of each type on one antenna is as follows : For males — 77 bristles, 

 3738 pegs, and 1718 pit pegs, and for females — 83 bristles, 2330 

 pegs, and 1362 pit pegs. From a superficial view, a pit peg re- 

 sembles a small circle (fig. 90, PPg), but when viewed in section 

 it is observed that a minute hair (fig. 91, PPg) with heavy walls 

 arises from the bottom of the pit, and a peg (fig. 92, Pg) arises 



