OF THE SPHINX LIGUSTRI. 
389 
nerves from each plexus in the abdomen unite with the principal nerve from 
the next ganglion [Plate XIII. fig. 1. (q, q , q, q)~\, while others ascend and ra- 
mify among the tracheae and dorsal muscles. The principal branch [fig. 1. 
(p, p, p, /?)] goes directly to the tracheae which come from the spiracula. In 
the thorax, the plexus from the hinder part of the second ganglion, [Plate XII. 
and XIII. fig. 1. (2, e),] unites some of its filaments with the nerve destined 
for the first pair of wings, while others are distributed among the muscles. 
The nerves from the plexus attached to the third ganglion give, in a similar 
manner, some of their filaments to the nerve intended for the second pair of 
wings, and some to the muscles. The second ganglion has the transverse 
plexus from the first, attached pretty closely to its anterior surface. This 
plexus distributes its nerves laterally to the muscles of the head and neck. It 
is also united by a small branch with the anterior lateral ganglia, [Plate XIII. 
fig. 2. (a , «),] and with the first pair of nerves from the second ganglion, [fig. 2. 
(k, k, l, /),] so as to form a complete link or medium of communication be- 
tween the nerves and ganglia of the head, neck, and second segment. From 
this it seems probable that these nerves may constitute the origin of a distinct 
system ; but whether this system in insects be analogous, either to the sympa- 
thetic or to the respiratory system of vertebrated animals, is yet a matter of 
inquiry. From the principal branches from each abdominal plexus being 
always distributed among the tracheae, near the spiracula, there seems reason 
for inclining to the latter opinion. 
Such is the arrangement of the nervous system when the larva has attained 
its full growth, and ceased to eat, preparatory to its changing into a pupa. 
This generally takes place at about the middle of August, or in the beginning 
of September. Some individuals undergo the change three weeks or a month 
earlier than others, owing to their having been developed from the egg at an 
earlier period; and the length of time they continue in the state of larva is 
about seven or eight weeks. The first symptoms of the insect being about to 
change to the pupa state occurs in its ceasing to eat, and after having re- 
mained quiet for a few hours, becoming exceedingly restless, and moving 
about with great rapidity. It then enters the earth, and forms an oval cell 
lined with a thin silky coating, and in it awaits its change. The delicate pea- 
green skin of the larva now becomes of a rusty orange colour, is shrivelled 
3 E 
MDCCCXXXII. 
