20 



balls they arc callod ganglia, and these ganglia differ in 

 composition from the nerve in having grey as well as white 

 matter. 



"We haTB seen that the larva is divided into thirteen 

 segments: the first segment forms the head, and contains 

 the brain, or a substance analogous to it ; the second 

 segment contains the first of these ganglia, and each con- 

 tains one down to the twelfth. These ganglia and large 

 connecting nervous cords may fairly represent the spinal 

 marrow. From these ganglia the nerves to the different 

 important organs proceed. The position of this portion of 

 the nervous system in insects lies along this under-surface 

 just below the oesophagus and stomach ; but in mamalia and 

 birds it is contained in the back-bone or spine. 



Diagram No. 1, figure one, shows its relative disposition. 

 The red nodules are supposed to represent the nervous 

 ganglia, and are only given this florid colour to show more 

 clearly their definite outline. Each, you will perceive, is 

 confined to its segment; but as some of these segments 

 will be nearly absorbed in the change from lava to pupa, it 

 will be necessary to observe and remember these ganglia 

 to understand how they adapt themselves to the altered 

 condition of the larval form. It would prove very little 

 interesting to you if I were to enumerate the dry details 

 of all these nerves that you see delineated. Some few it 

 is necessary I should point out. Vide diagram. 



Vfe have now shown a rough and general distribution of 

 the nerves ; but there is one peculiarity about the nervous 

 system I may mention, that these ganglia, I believe, with 

 whatever other vital powers they possess, are the reservoirs 

 for that peculiar principle which is collected during the 

 hours of repose to sustain, and in the active duties, pleasures, 

 and pursuits of every- day existence. If undue exertion be 

 called forth early in the day, this nervous laboratory is 

 exhausted before its regular time, and a consequent desire 

 for repose is absolute. But be this as it may, there is one 

 certain fact established, that the nervous system is in pro- 



