THE OLFACTORY ORGANS OF DIPTERA 477 
section. In figure 30 the row was cut crosswise, passing longi- 
tudinally through the shtlike aperture, whereas in figure 31 the 
row was cut lengthwise, passing transversely through the slitlike 
aperture. 
Figure 32 is a drawing, showing a portion of the base of the 
halter in perspective and in section, it was cut crosswise in the 
direction of line BB in figure 3. The muscle (MV) and chordotonal 
organ (ChO) are drawn in only their approximate positions as 
represented by Weinland; their points of attachments are incor- 
rect. The scalpel pores (nos. 14 and 18) and a few basal 
pores (no. 15), shown both in perspective and in section, lie on 
Figs. 30 and 31 Schematic drawings of a portion of a scalpel row on halter of 
Musca domestica, showing the row in perspective and in section. In figure 30, 
the row was cut crosswise, longitudinally through the slitlike aperture, while in 
figure 31 the row was cut lengthwise. Thenerve (N) is drawnin perspective, and 
gtrong pseudohairs (Hr!) bend over the pores, protecting them well. 
curved plates, and it is noted that the surface of the base of the 
halter is very rough, being made up of minute hills and hollows. 
In Weinland’s drawings it is noted that the nerve does not run 
beyond the olfactory pores on the halter, but the trachea runs 
into the peduncle and stops there. <A cross-section of the knob 
of a halter somewhat resembles a double convex lens; it contains 
masses of cells which are certainly not sensory, but probably they 
are the remains of the early hypodermis. The surfaces of the 
knobs of prepared halteres bear a few true hairs, and they are 
generally smooth excepting the folds (fig. 3, 7), caused by pre- 
paring the specimens. 
