476 N. E. McINDOO 
drawn in figure 29 (BPor.). Figure 26 represents a section pass- 
ing transversely through four rows and longitudinally through 
one row of scalpel pores. In the latter pore, as well as in figures 
27, 28, and 29 (SPor:), the pore ridge (PorR) and pore link 
(PorL) can be identified. Figure 29 represents an oblique longi- 
tudinal section through the base of the halter in the direction. of 
AA in figure 3. The large nerve (N) is very conspicuous; it 
spreads out fanlike and connects with the masses of sense cells 
Fig. 29 Longitudinal section (} diagrammatic), cut in direction of line AA in 
figure 3, through base of halter of Musca domestica, showing internal anatomy, 
sealpel pores (nos. 14 and 18), basal pores (no. 15) and Hicks’ pores (no. 16). 
The chordotonal organ (ChO) is only in its approximate position and was copied 
from Lee (’85). One row each of basal pores (BPor,) and scalpel pores (SPor,) 
cut lengthwise, and 3 rows of basal pores (BPor:) and 5 rows of scalpel pores (no. 
18) were cut crosswise. Ch, internal view of chitin; Ch2, external view of chitin; 
M, muscle; N, nerve; SC, sense cell, and Tr, trachea. X 500. 
(SC). A trachea (7'r), muscles (/) and a chordotonal organ 
(ChO) are also present. Both Lee and Weinland have studied 
the chorodotonal organ, but the present writer has paid little 
attention to it, hoping later to make a special study of this type 
of sense organ. In figure 29 it is represented in only its approxi- 
mate position as drawn by Lee. 
Figures 30 and 31 are schematic drawings of a portion of a row 
in a scalpel group, showing the pores both in perspective and in 
