66 Nervous System of Insects. 
the last three abdominal, when there are in all thirteen (Fig. 
18). In the pupa, the last two of the thorax, and the first 
two abdominal, unite into the twin-like post-thoracic (Fig. 
16), which supplies the meso, and meta-thoracic legs, and 
both pairs of wings with nerves. The fourth and fifth 
ganglia also unite, so that the adult worker-bee has nine 
Fic. 18. 
Nervona System of Workew Larva, aftey Duncam 
ganglia in all, The brain, like our own, is inclosed in 
membranes, is composed of white and gray matter, and 
is undoubtedly the seat of intelligence. Hence, as we 
should suppose, the brain of the worker is much larger 
than that either of the drone or queen. The ganglia 
along the cord are the seat of reflex acts the same as 
is the gray matter of our own spinal cord. Indeed, the 
beheaded bee uses its members much more naturally than 
do the higher animals after they have lost their heads. 
This may arise from their more simple organism, or 
from a higher development of the ganglia in question. 
The organs of circulation in insects are quite insignifi- 
cant, The heart (Fig. 19, 2) is a long tube situated along 
the back, to which it is held by large muscles (Fig. 19, 7), 
