546 
MR. NEWPORT ON THE RESPlkATION OF INSECTS. 
the transverse nerve (e), passes outwards over the smaller rectus, at the outer margin 
of which it gives off its first branch ( p ), which is directed backwards. It then passes 
between the third and fourth oblique, and gives off its second branch (q), which is 
directed forwards, and a little further outwards its third (r) and fourth (5), which are 
directed backwards. The trunk of the nerve then crosses the longitudinal trachea, 
and unites with a short nerve from the posterior division of the transverse nerve (n). 
It then divides into two branches ( t ), which pass upwards between the dorsal recti 
and oblique muscles, where they again divide into many branches. About midway 
across the dorsal recti some of the branches interweave with each other, and form a 
small plexus (w) before they are distributed to their proper muscles. It is the first 
two divisions of this great nerve which particularly claim our attention. The first 
division (p) passes backwards beneath the greater rectus, and divides again into two 
branches. The anterior one ( v ) is given to the four oblique muscles, and to the 
under surface of the rectus, which are thus shown to be supplied by two sets of 
nerves. The second division passes backwards and is again subdivided ; the poste- 
rior division being given to the under surface of the smaller rectus, and to the lower 
portion of the great oblique, while its termination (tv) is continuous with a portion of 
the second branch of the transverse nerves ( h ). Some of the branches of this nerve 
pass between the triangular and second oblique muscles (-r), and are given to the 
latero-abdominal. The second branch of the main trunk of this nerve ( q ) passes ob- 
liquely forwards and outwards beneath the great oblique, and gives off first a small 
branch to the transverse abdominal muscles ( y ), and a little further on a second 
branch, one portion of which is also given to the transverse and latero-abdominal 
muscles ( z ), and another which passing more directly outwards supplies the latero- 
abdominal (31) and the oblique great constrictor of the spiracle (25), and divides 
behind the spiracle into two terminal portions, one of which is given to the retractor 
valvulse (27), and the other, which passes forwards, to the transverse lateral mus- 
cles (24), which, as before stated, are supplied by two distinct sets of nerves. The 
divisions of this last portion of nerve are particularly interesting. Before dissecting 
these nerves I had conceived that the great constrictor of the spiracle and retractor 
valvulse muscles were probably supplied by the transverse nerves, and hence was 
much surprised to find that they were supplied from the great moto-sensitive nerve 
from the ganglion of the cords, by which they are thus endowed with voluntary power 
and sensation. But upon reflection it will be seen that this ought really to be the 
case. To enable the insect to make a forcible expiration and close its spiracle, which 
is evidently an effort of the will, the great constrictor of the spiracle ought to be en- 
dowed with voluntary power. On the other hand, since the insect has a voluntary 
power of closing, it must also have a similar power of opening the orifice, and conse- 
quently the retractor valvulse ought necessarily to be supplied from the same source. 
There are, however, a few filaments given from the transverse nerves to these muscles, 
and to the orbicular which surrounds the spiracle. The remaining portion of the 
