390 
MR. NEWPORT ON THE NERVOUS SYSTEM 
and contracted, and is often covered with moisture. At this period all the 
nerves belonging to the ganglia of the first five segments are directed for- 
wards, [Plate XII. fig. 1 .,] while the lateral nerves from the ganglia in the 
posterior segments are disposed with some irregularity. If the larva be pre- 
vented from undergoing its metamorphosis, by having been removed from its 
cell in the earth, and also prevented from remaining at rest, the nervous 
system is but little altered. But the change can be retarded only for two or 
three days, when the insect, upon being allowed to remain at rest for a short 
period, entirely loses the power of locomotion, becomes much shortened and 
contracted, and in its general appearance resembles the future pupa. When 
the period of change has arrived, the larva forces an opening through its skin, 
along the dorsal part of the third and fourth segments, and by repeated efforts 
continues it forwards as far as the head, the covering of which separates into 
three pieces. The head and trunk of the new pupa, with all their parts sepa- 
rate, but encased each in a very delicate skin, and nearly as fluid as water, 
are then gradually withdrawn from beneath the old covering, and disposed 
along the under surface of the body, while the skin itself, by repeated con- 
tractions of the abdomen, is forced up together, and entirely slipped off at the 
anal segment. The new pupa then lies at rest, and the coverings of its limbs 
and body adhere together and form a hard case, capable of preserving it from 
injury. During this, its nervous system is also changing, by the cerebral 
lobes being increased in size, and the eleven ganglia brought nearer together, 
by the shortening which is taking place in their respective segments, so that 
the longitudinal cords lie in a very irregular manner between the ganglia, 
while the ganglia themselves are confined in their proper places in the seg- 
ments by the nerves running transversely from them. 
If the insect be examined about two hours previously to its bursting the 
exuviae and becoming a pupa, the change in its nervous system is very evident, 
[Plate XII. fig. 3.] The lobes above the oesophagus have assumed more the 
appearance of a cerebral mass, [fig. 3. (a),] and are increased in diameter, while 
the cords descending from them are shortened and thickened. The nerves for 
the antennae are enlarged, and lie folded on each side the head, and the optic 
nerves have undergone considerable alteration. Instead of being simple cords, 
they are now so much shortened and thickened, as to be hardly distinguish- 
