52 ANTHON. [Vor. XIX. 
on 
of the body wall and the alimentary canal, and the commis- 
sures must be able to stand the strain. 
From these two main lateral branches ramifications pass 
off into every part of the body. (Fig. 37.) These branches 
pass among the different organs of the body and seem to 
serve somewhat as strands to hold them in place. These 
branches have very minute ramifications, which become so 
attenuated that they pass among the fibers of the muscles. 
Each of the main trachez at the anterior extremity breaks up 
into a number of fine fibers, most of which are connected with 
the brain. In the last segment, just above the hinder part 
of the heart, there arises a number of small branches which 
are connected with the stigmata. 
The lining membrane of the trachez consists of a layer of 
polygonal cells fitting closely together as a pavement epithe- 
lium. The chitinous wall or intima is thickened at intervals 
to form thread-like ridges, the teenidia. These tznidia serve 
to keep the tracheze open without affecting their flexibility. 
There is but one pair of spiracles so that the larva is 
metapneustic, as is the case with nearly all the Tipulide. 
The prominent oval spiracles are inserted at the apex of the 
last segment, and turn backwards and upwards. The struc- 
ture of the spiracles is very similar to that of the larve of 
Dicranota and Phalacrocera, as described by Miall and Shel- 
ford. (Fig. 38.) The central portion of the spiracle consists 
of an inner cone or plug, which is surrounded by a thick and 
solid chitinous wall. Outside of this is a chamber with a 
colorless chitinous wall, the vestibule. The cavity of the 
vestibule is crossed by many radiating fibers, which are irregu- 
larly branched and start from the outer wall. Some of the 
fibers connect with the inner cone, but many do not reach :t 
at all. The stigma forms the outer end of an air chamber 
whose inner surface is lined with a zone of large cells. This 
region is evidently of great importance in the respiratory 
mechanism of the larva, as there are great masses of blood 
corpuscles lying about the spiracle. There is a circular mus- 
cle with which to draw in the spiracle and help bring the 
