1929 ] 
Tracheal System of Pyrausta nubilalis 
337 
three transverse connections crossing the ailmentary tract 
between the prothoracic spiracles. 
Peterson (1912), in the tomato-worm, finds that in all 
cases except the transverse tracheae described above, the 
cross tracheae lie ventral to the nervous system. This is 
not always true in Pyrausta nubilalis. 
Just behind the prothoracic spiracle there is a trachea, 
which I have numbered 1. This lies on the inner surface of 
the muscle layer. It crosses the nerve cord dorsally, ter- 
minating, usually, in the prothoracic ganglion. Near the 
base of the ganglion the trachea meets the corresponding 
trachea from the other side, and a cross connection, dorsal 
to the nervous system, and ventral to the alimentary tract, 
is formed (Fig. 10). Trachea 1 varies. It may be much 
reduced, forming only a very weak connection with the 
central nervous system, with the corresponding trachea 
of the opposite side entirely absent (Fig. 11). Sometimes 
the trachea to the ganglion is obviously from the left side, 
with the trachea from the right meeting it (Fig. 12), and 
sometimes the opposite is true. The branches from trachea 
1 usually supply the muscles, but in one specimen a large 
branch ran to the nerve cord in front of the mesothoracic 
ganglion. (Fig. 13) . In the figures the size of the tracheal 
connections with the ganglion is exaggerated. 
Trachea 1 lies, apparently, at the junctions of the longi- 
tudinal muscles of the prothorax with those of the meso- 
thorax, and is a useful landmark in locating the limits of 
these segments. 
The next transverse trachea I have numbered 2 (Fig. 14) . 
It lies in the mesothorax on the outer side of the muscle 
layer. It passes beneath the central nervous system just 
in front of the mesothoracic ganglion. In relation to the 
muscles and the nervous system and to tracheae 1 and 3, 
which will be described next, it is, if not homologous to 
trachea 2-a, analogous to it. 
Trachea 3 lies on the inner surface of the muscle layer 
and approximately marks the limits of the mesothorax be- 
hind and of the metathorax in front. It is a transverse 
trachea much as is trachea 1. A branch to the mesothoracic 
ganglion meets a branch from the opposite side, forming a 
