L. Harrison 
105 
twigs among the muscles. Similarly at the hind end of the abdomen the 
main trunks continue backwards beyond the last stigmatic branch, and 
break up into fine twigs dorsal to the rectum. 
The tracheal branches of the head have the general arrangement 
shown in the figure. The most posterior pair of branches comes ventrally 
from the main trunks in the anterior part of the prothorax, and the 
branch of each side turns outwards and breaks up among the temporal 
muscles, both dorsal and ventral. Just within the head, small branches 
are given off internally to the oesophagus. Two large branches on 
either side run out to the lateral regions of the head. At the level of 
the anterior cornua of the brain each main trunk divides into dorsal 
and ventral branches. The dorsal gives off an internal branch which 
serves the pharynx and brain; and is continued forwards to the dorsal 
region of the forehead. The ventral gives off an internal branch which 
meets its fellow of the opposite side to form a commissure running 
along the anterior margin of the tentorium; and runs forwards and down¬ 
wards itself to be distributed to the mouth-parts. Part of the internal 
dorsal branch of either side passes up through the gap between the cornua 
of the brain, dividing into two, so that four vessels run longitudinally 
backwards closely applied to the brain, giving off smaller branches 
which ramify over the surface. 
In the prothorax a triangle is formed internal to each stigma, as 
already stated. The main trunks here lie nearer the dorsal than the 
ventral surface, and in front of the triangles a commissure descends 
ventrally so as to underlie the prothoracic ganglion, which is innervated 
by small branches from it, and gives off two branches to each prothoracic 
leg. The mesothoracic commissure comes off from the outer sides of 
the triangles, passing downwards and backwards, and exhibiting 
precisely the same relations towards the mesothoracic ganglion and 
legs. The metathoracic commissure lies at the back of the segment, 
passing below the crop, and innervates the corresponding ganglion and 
legs. I can find no indication whatever of the survival of any remnant 
of wing tracheae, unless the inner sides of the triangles can be looked 
upon as such. Nor is there any indication of stigmata, or of stigmatic 
branches, in either meso- or metathorax. 
Metameric arrangement of the tracheae, which was not obvious in 
the head and fairly well marked in the thorax, becomes much more 
definite in the abdomen. The typical constituents on each side of any 
segment are (a) the portion of the longitudinal trunk contained within 
the segment; (6) the stigmatic branch; (c) the ventral branch; (d) the 
