MR. NEWPORT ON THE RESPIRATION OF INSECTS. 
547 
trunk of this nerve passes forwards and outwards, crosses the retractor of the spiracle, 
and then gives off its third branch (32), which is almost immediately again divided, 
and sends one portion backwards to the transverse abdominal ( 17 ) and anterior 
abdominal (18), and the other forwards to the transverse lateral muscles (23). The 
remaining portion of the nerve continues its course over the transverse lateral, and 
terminates in the muscles of the back. 
The second or oblique moto-sensitive nerve (33) from the cords and ganglia is 
much smaller than the first, the one we have just described. It passes diagonally 
outwards and backwards, and divides into two principal branches. The first passes 
outwards, and is given to the latero-abdominal muscles, which contract the diameter 
of the segment. One portion of the second branch supplies the triangular and trans- 
verse median muscles, while the other (k) passes downwards and outwards and unites 
with a portion of the third branch of the transverse nerves (*), as before stated. 
From this distribution of the nerves it is evident that some of the muscles are sup- 
plied from two sources, and it can hardly be doubted that these have distinct func- 
tions. The remarkable fact that the transverse nerves appear almost exclusively to 
supply the tracheae, while the moto-sensitive, which come from the motor tract and 
ganglia, and communicate volition and sensation, supply the muscles, even of the 
spiracles, cannot escape our observation as a striking proof that these nerves are of 
distinct functions. When we connect these facts with that of the longitudinal portion 
of the transverse nerves in each segment deriving a few filaments from the motor sur- 
face of the cords, and with that of filaments from the transverse nerves being distri- 
buted to some of the muscles in addition to nerves derived from the cords and ganglia, 
we can scarcely hesitate to assent to the opinion that while the transverse nerves con- 
nect the voluntary with the great organic functions of the body, they are more sub- 
servient to the latter than to the voluntary or animal powers. 
The Manner in which Respiration is performed. 
It has been shown that in every act of respiration in insects nearly all the muscles 
and nerves of each segment of the body are brought into consentaneous action, as the 
muscles of the chest and ribs in vertebrated animals, like which the insect is able to 
make either a forcible expiration, as during pain, and perhaps also during transfor- 
mation, or can take a forcible inspiration at the instant of any sudden exertion. The 
manner in which the air is renewed in the trachea has excited some inquiry, but no 
satisfactory explanation of it has yet been given. Some have supposed that the dila- 
tations and contractions of the dorsal vessel contribute towards it, others that simply 
the opening and shutting of the spiracles, the extension and contraction of the body, 
the presumed elasticity of the air-sacs, or the sliding of the segments one over the 
other, may be the means of effecting it*. But neither of these actions could alone 
induce a current, or succession of currents of air to be sent over the whole body, 
* Carus, Introduction to Comparative Anatomy, vol. ii. p. 167, translated by Gore. 
4 a 2 
