392 
MR. NEWPORT ON THE NERVOUS SYSTEM 
there is a small aperture for the passage of the oesophagus. All the ganglia of 
the thorax are much enlarged, and the first pair of nerves which belonged to 
the second ganglion in the larva, now appear to take their origin from the 
cords, [fig. 5. (2, c),] and after anastomosing with the second pair, to form with 
them a plexus which supplies the neck and collar; while the third pair pass 
as before to the muscles of the first pair of legs, [PI. XII. fig. 5. (2, d).] The 
first pair from the third ganglion, and the roots they derive from the cords, are 
much enlarged, [fig. 5. (3,/),] as also are the second pair given to the second 
pair of legs. But the greatest alteration is in the fourth ganglion, [fig. 5. (4),] 
which is now more than double its former size, is elongated and bilobate, and 
gives off four pairs of nerves. The first, with the roots they derive also from 
the cord, are given to the inferior wings ; the second, to the third pair of legs ; 
the third pass backwards to the muscles of the abdomen ; and the fourth are 
directed upwards, divided into three branches, and are distributed to the poste¬ 
rior muscles of the trunk. The fifth ganglion is close to the fourth, [fig. 5. (5),] 
and coalesces with it; the nerves last described being those which originally 
belonged to it. The sixth ganglion, [fig. 5. (6),] much decreased in size, is often 
found at this period close to the fifth, from which it is separated only by a 
slight indentation. It is more frequently, however, at a short distance from 
it. The longitudinal cords are no longer irregularly folded in the abdomen ; 
they now lie in a direct line between the ganglia, [fig. 5. (7, 8, 9, 10, 11)] ; 
but neither these nor the cord itself are increased in diameter. 
It is thus evident that the principal part of the change in the nervous system 
of this insect occurs during the first month of the pupa state, and that it is not 
regularly progressive, but takes place at intervals. Upon what these apparent 
irregularities depend it is difficult to determine. Perhaps they may be the 
result of a partial exhaustion of the vital powers, during the effort of transfor¬ 
mation, and which require an interval of repose to re-establish their activity. 
Thus we find, that during the first four days of the pupa state, there is but little 
alteration of structure, beyond what exists at the actual period of changing from 
the larva ; the energy of the insect having been partially exhausted during the 
effort of transformation. But when it has remained for some time at rest, its 
energy is restored, and the change again advances. That such is in reality the 
case seems to be supported by the fact, that when a larva has become so ex- 
