ANATOMY AND PHYSIOLOGY. PD] 
the body, from between the eyes to the root of the 
sting. In the larva there is a knot or ganglion—we 
had better retain the use of this word—for each seg- 
ment. But in the perfect insect the ganglia are 
changed, like the segments, according to the import- 
ance which the several parts have assumed in the 
imago. Some shrink up and coalesce, others are much 
enlarged. The two first ganglia are closed up 
together to form the brain, and so the cesophagus, 
passing between the two threads, seems to perforate 
the brain. From the brain, nerves are given off to 
the eyes and to the antenne. Thence the double cord 
descends, and passes along the lower side or, as we 
should call it, the front of the body, in the middle 
line, giving off at each of the ganglia nerves of motion 
and sensation, according to the various requirements 
of the adjacent parts; just as we see in the abdomen, 
only on a much more extended scale. The position of 
the spinal cord in front, instead of at the back of the 
insect, may seem as great an anomaly compared with 
our own structure, as the passage of the oesophagus 
through the centre of the brain. But it is the whole 
arrangement that is altered, not the relative position 
of these parts only. The cord is not merely pushed 
forward ; it is turned round, so that the motor strings 
are still, as in Vertebrate animals, placed towards the 
interior, and the sensorial portion of the cord lies next 
the surface of the body. And the limbs too have 
changed their relations to the frame on which they 
are hung, as well as the spinal cord. For, as 
Burmeisterf reminds us, the extremities, which in the 
higher animals are dependent on the spine, are in 
* ‘Entomology,’ translated, p. 272, 
