INSECTS 123 



5. Nervous System 



The nervous system of the Grasshopper is closely similar in its 

 general structural features to that in the Crayfish where, it will be 

 remembered, there is a reduced number of ganglia on the ventral 

 nerve cord so that they do not exactly conform to the body seg- 

 mentation. 



The ventral nerve cord of the Grasshopper lies in a median line 

 close to the ventral body wall. The double nature of the cord is 

 clearly evident except at the points where the ganglia are present. 

 Altogether there are ten ganglia present, two of which are in the 

 head, three in the thorax, and five in the abdomen. Of these, the 

 cerebral ganglion, which constitutes the brain of the animal, is 

 the largest and possibly the most important. The third thoracic 

 ganglion is also very large and of great importance in the innerva- 

 tion of the wings and the last two pairs of legs. 



Sense Organs. In general, the sense organs of all the Insects 

 are much the same and accordingly we shall consider them in con- 

 nection with our study of the Bee, in which they are very highly 

 developed. However, mention at this point should be made of the 

 organs of hearing in the Grasshopper which are particularly well- 

 differentiated. A pair of these organs is present on the first seg- 

 ment of the abdomen, one on each side of the body. Each 'ear' 

 consists of an oval-shaped plate, or tympanum, which is embedded 

 in the body wall at the surface. Underneath the tympanum is a 

 small pit with sensory cells from which a nerve extends to the third 

 thoracic ganglion. Stimuli arising from the vibrations of the tym- 

 panum are transmitted over the nerve to the ganglion. 



II. HONEY BEE 

 A. External Structure 



In an active colony, or hive, three types of Bees are found which 

 differ both in their structure and in their functions to the colony 

 as a whole. There are several hundred fertile males, the drones, 

 one fertile female, the queen, and several thousand infertile 

 females, the workers. In the fall when the active period of the 

 colony is over for the season, the drones are expelled from the hive 

 and die, so that only the workers and the queen remain in the hive 

 throughout the year. 



