118 
The Respiratory System of Mallophaga 
The posterior commissure described above for Heterodoxus is also 
present in Trimenopon, Nesiotinus, and some species of Trichodectes; 
and is figured by Mjoberg (1910, p. 218) for Eutrichophilus. It may 
be present in Trichodectes setosus, which Neumann (1913, p. 623) claims 
to be identical with Mjoberg’s species of Eutrichophilus, but I have not 
been able to make it out in ordinary preparations. It is of the same 
diameter as the main trunks, thus differing from the neural commissures, 
which are distinctly narrower. Its presence in so many genera that 
otherwise exhibit primitive characters, as well as its universal occurrence 
in the Anoplura, leads me to look upon it as a primitive character also. 
It is not found in the more specialised genera. 
Fig. 20. Prothorax and head of Gyropus ovalis, to show superficial ventral tracheae. 
Tetrophthalmus is remarkable for having a broad commissure in 
the fourth segment; but this is not worth stressing, as it is probably 
directly connected with the very extraordinary change in habit of the 
species of the genus. 
In all species of which I have examined fresh material, I find a great 
constancy in the arrangement of the whole tracheal system. The four 
neural commissures are always present; as are the prothoracic tri¬ 
angles ; and the chief variations are only in detail of the dorsal and 
ventral system of branches. Gyropus and Gliricola have alone afiorded 
exceptions. Fig. 20 shows the ventral superficial tracheae of G. ovalis, 
from which it will be seen that there are two head commissures, and 
