THE POPULAR INSECT PLAN 



211 



The Nervous System 



The nervous system of the bee is well developed, consisting of a 



series of ganglia, forming a double ventral nerve cord with a dorsal 



cerebral ganglion (brain), 



antennal . 



rain. 



optic loloe 



to -vin^? 



to leg 



connected by a circum- 

 esophageal nerve ring with 

 a subesophageal ganglio7i 

 directly underneath it. 

 Although typically in a 

 segmented animal there 

 should be one ganglion 

 for each segment, we find 

 fewer ganglia than seg- 

 ments in the adult bee. 

 This is because certain of 

 the ganglia have fused, 

 there being seven in the 

 ventral ner^'e cord of the 

 bee. From each of these 

 nerves efferent fibers ex- 

 tend to the muscles while 

 afferent fibers from sense 

 cells end in the ganglia to 

 make up the reflex arc 

 previously described (page 

 195). Not all co-ordi- 

 nation of muscles is controlled by the brain, for a headless bee will 

 still walk and experiments have shown that the body ganglia are 

 independent centers of control over the appendages. Insects of the 

 order Hymenoptera, to which the bee belongs, have the best brain 

 development of any of the insects, a fact that seems to be correlated 

 with their complex social habits and their keen senses. 



Nervous system of worker bee. Why are the 

 ganglia in the thorax so much larger than those 

 of the abdomen? Note that the brain is on the 

 dorsal side, the esophagus (not shown) passing 

 between the two nerves that connect it with the 

 first thoracic ganglion. (After Snodgrass.) 



Reproduction and Life History 



Although the workers possess undeveloped ovaries, all the eggs are 

 laid by the fertile female or queen. While a worker may live about 

 six weeks in summer and never more than a few months, the queen 

 lives three or fotir years, or even longer. The ovaries of the queen are 

 made up of a number of tubules, in which are eggs in all stages of 



