1929 ] 
Tracheal System of Pyrausta nubilalis 
335 
second pair of spiracles thus loses its connection with the 
general respiratory system and ceases to function. 
That means that the apparent branch in the metathorax, 
arising from the apparent main trachea and passing be- 
neath the muscle, is, in fact, the main trachea, and the 
apparent main trachea is a branch. But it is hard to 
explain the tracheal branchings in the mesothorax on this 
basis. 
The branch from the first abdominal spiracle passing 
forward beneath the sterno-tergal muscle, does not, in 
Pyrausta nubilalis “lose itself among the dorsal muscles/’ 
but becomes a part of the dorsal longitudinal system, send- 
ing branches to the metathoracic leg and to the wing-bud. 
Figure 5 and figure 6 show the branches arising from 
the first and fourth abdominal spiracles, respectively. In 
the case of the branches arising from the first abdominal 
spiracle it is evident that the presence of the appendages of 
the metathorax, legs and wings, has made necessary more 
tracheal branches than are called for in the fourth segment 
where such appendages are absent. 
But a study of the branches arising from the fourth 
abdominal spiracle fails to show any that takes over the 
role of the main trunk, if we consider that the branch from 
the first abdominal spiracle from which spring the tracheal 
supplies to the alimentary tract, the w T ing-bud, and leg, 
to be the anterior branch, or “main tracheal trunk” from 
that spiracle. 
The apparent main tracheae, the “lower visceral branch” 
of de Guyse, does not meet the posterior branch from the 
prothoracic spiracle until after it throws out branches 
in the mesothorax that are at least analogous with the 
branches from the first abdominal spiracle. (Fig. 7). It 
is rather difficult to see how these branches arose as sec- 
ondary branches from the lower visceral branch from the 
first abdominal spiracle and the posterior branch from 
the prothoracic spiracle. 
The Transverse Tracheae 
The longitudinal tracheae of each side are connected by 
transverse tracheae in every spiracle bearing segment, ex- 
