MR. NEWPORT ON THE RESPIRATION OF INSECTS. 
543 
anterior lateral ganglia, which are contained within the head, or first segment, and 
are analogous to the superior cervical ganglia ; and Professor Muller, in his paper 
upon the Sympathetic or Visceral Nerves of Insects, has expressed his doubts with 
regard to its existence as described by De Serres. Muller regards the nerve which 
I have described on a former occasion as the vagus, as analogous to the sympathetic; 
but there are many points which seem opposed to this opinion. The vagus, or re- 
current nerve of Lyonet, is exceedingly small in almost every insect when compared 
with the size of the organs unto which it is distributed, especially when we compare 
those organs, and the nerves which supply them, with the corresponding parts of the 
human body. Besides which I have never been able to trace the nerve along the 
alimentary canal beyond the middle portion of the stomach, where it seems to be lost 
in the same manner as in Man and other Vertebrata. 
With regard to the cords themselves, it was long ago suggested by Weber that the 
ganglia, which we now find to exist entirely in the sensitive tract in insects, are ana- 
logous to the intervertebral ganglia of Vertebrata. Hence the analogy between the 
spinal cord of Vertebrata and the abdominal cords in Invertebrata is very nearly 
proved. The very great analogy between the origin, course, and situation of the vagi 
nerves in Man, and the corresponding one in insects, clearly demonstrates the iden- 
tity of the structures. Carus* has made some observations which lead us to con- 
sider whether the oesophagus and crop in some volant insects are not somewhat con- 
cerned in the function of respiration, since it is well known that every part of the 
alimentary canal is profusely supplied with tracheal vessels, and especially when we 
remember that the vagus is the chief nerve of the organs of respiration in Man. I 
shall therefore go more particularly into a description of this nerve in insects. 
In all lepidopterous insects it has two distinct origins, one from each crus, which 
descends from the base of the cerebral ganglia or lobes of the brain. These origins 
are analogous to the two vagi nerves in Man, but instead of continuing separate and 
passing down one on each side of the oesophagus, they pass at first a little forwards 
and inwards, and unite above the palate, where they form a ganglion. Here also we 
have some analogy with the nerve in Man. The vagus nerve, after its junction with 
the spinal accessory, passes forwards and out of the skull through the foramen lacerum 
posterius, and there forms a slight enlargement almost precisely corresponding in 
situation to the point abuve the palate and pharynx, where the ganglia would have 
been situated on the nerves had the two vagi nerves in Man been united. From the 
ganglion thus formed by the union of the two roots of the vagus nerve in insects, the 
two approximated origins thus forming one trunk pass backwards along the median 
line of the oesophagus beneath the anterior portion of the dorsal vessel. A little behind 
the brain the vagus is united by filaments with the anterior lateral or cervical ganglia, 
which are analogous to the superior cervical of the sympathetic in Man. Here there 
is an analogy between the union of these ganglia and the vagus in insects, and the 
* Comparative Anatomy, translated by Gore, vol. ii. p. 166. 
