MR. NEWPORT ON THE RESPIRATION OF INSECTS. 
541 
These are the muscles which more particularly claim our attention, in order that 
we may see what nerves are distributed to them, and consequently what nerves are 
most concerned in respiration. 
Nerves concerned in Respiration. 
The nerves concerned in respiration, like the muscles, include those of the whole 
segment. In a former paper I have particularly described those nerves which, from 
their distribution, were considered to be more especially concerned in respiration. 
My endeavour now is to trace these and the moto-sensitive nerves to their termina- 
tions in the different layers of ventral and lateral muscles. 
The inverted position of the nervous cords in insects and other Invertebrata has 
not a little confounded the right understanding of the analogy which exists between 
the nervous cords of vertebrated and invertebrated animals, and has given an appear- 
ance of probability to the opinion entertained by some anatomists that the cords in 
Invertebrata are not analogous to the spinal cord of Vertebrata, but to the sympathetic 
system. Even some of those who now believe that these cords are really analogous 
to the cerebro-spinal system of the higher animals, can hardly reconcile this opinion 
with the fact of their being situated along the ventral instead of the dorsal surface of 
the body. The reason for this change of position of the cords in Invertebrata ap- 
pears to be partly to protect the cords themselves, and partly that the nerves may 
be supplied to the limbs without having to travel round the sides of the body, and 
thereby be exposed to the hazard of injury, which they would be were they situated 
along the dorsal surface as in Vertebrata. But notwithstanding this change of 
position of the cords in Invertebrata, — since we now find that they are composed 
each of two tracts, as in vertebrated animals, — it is interesting to observe that these 
two cords, and the tracts of which they are composed, bear the same relative po- 
sition to the viscera and to the exterior of the body as in Man and other Vertebrata. 
Thus the cord which runs along the ventral surface in Articulata has its motor 
tract nearest to the viscera (a), or most internal, the same as in the human subject ; 
while the sensitive tract, which possesses the ganglia, lies along the under surface of 
the cord, and is nearest to the exterior of the body, just as the sensitive tract with 
its ganglia in Man lies nearest to the cutaneous or external surface. It will thus be 
seen that the two tracts maintain the same relative position with regard to each other, 
as well as to other parts of the body, in both divisions of the great kingdom of ani- 
mated nature, whether the actual situation of the cords be along the dorsal or ventral 
surface of the body. This being the case, it leads us to consider the propriety of 
the terms anterior and posterior tracts or columns , as applied to the motor and sensi- 
tive tracts of the nervous system, and whether it would not be advisable entirely to 
abandon these terms, and designate the two columns external and internal , the sensi- 
tive the external, and the motor the internal column, since these terms would be 
strictly applicable to the situation or position of the columns in all classes of animals. 
