THE METAMORPHOSES OF THE NERVOUS SYSTEM. 39 
The beetles (Coleoptera ) , the locusts ( Orthoptera ), and the bees 
(. Hymenoptera ), do not have their thoracic ganglions all fused 
into one mass when they attain adult age, and the nervous 
centre, which is known as the first of the thoracic segments — 
the prothorax — never unites v/ith the others. But the next two 
ganglions do become fused together in those species which attain 
great perfection of organisation. In the larva of the bee the 
three thoracic nervous centres are like those of the silkworm 
caterpillar, but in the perfect insect these ganglions enlarge, and the 
hindermost are confounded together. This concentration does 
not exist in all adult insects, and the ganglions remain separate 
in most of them. 
The nerves which supply the muscles of the first pair of 
legs in the perfect insect arise from the first ganglion of the 
thorax or the prothoracic. Those destined for the innervation 
of the first pair of wings and the second pair of legs come from 
the mesothoracic nervous centre, and the metathoracic enlarge- 
ment originates the nerves of the third pair of legs and of the 
second pair of wings. Nothing appears to interfere with this 
relation between the ganglions and the legs and wings. 
A great number of larvae have nine pairs of ganglions in the 
abdomen, and this arrangement often persists during adult age ; 
as a rule these nervous centres are small, and they even remain 
detached in pairs in some imperfect insects. In the caterpillar 
of the silkworm there are eight ganglions in the abdomen. Seven 
of them are located in the anterior seven segments, and the eighth 
is situated near the front part of its body ring. It is very large, and 
evidently is composed of two nervous centres united. But in any 
other insects whose development is less advanced, the eighth and 
ninth abdominal ganglions are found to occupy their corresponding 
segments. The size of the nerves which pass off on either side from 
the ganglions in the abdomen of the larva, is usually much less 
than that of the twigs which arise from corresponding situations 
in the perfect insects. The lateral nerves have much to do with 
the respiratory efforts, which are feeble in most larvae, but very 
vigorous in the perfect adult insects. There is no comparison 
to be entertained between the amount of the breathing energy 
of a sluggish maggot, grub, and caterpillar, and that of a lively 
