14 PHYLUM ARTHROPODA 



seen to be double and to contain, in the abdomen, five enlarge- 

 ments, the ganglia, from each of which fine nerves radiate. Trace 

 the nerve cord from the abdomen into the thorax. It is here pro- 

 tected by hard projections of the body wall, which must be care- 

 fully removed. Four large ganglia will be found here, the three 

 posterior ones of which are the thoracic ganglia. The one in the 

 forward portion of the prothorax really belongs to the head and 

 is called the suboesophageal ganglion. From it a pair of nerve 

 connectives passes to the dorsally situated supraoesophageal 

 ganglion, or brain. The brain is the largest ganglionic mass in the 

 body and is situated in the top of the head between the eyes. Lay 

 bare the brain. Notice the optic lobes going to the eyes, and be- 

 tween them the much smaller ocellar lobes sending nerves to the 

 lateral ocelli. Beneath the optic lobes are the antenna! lobes, 

 which send nerves to the antennae ; near them in the median line 

 is the median ocellar lobe, which sends a nerve to the median 

 ocellus. 



Exercise 15. Make a large sketch of the nervous system as far as 

 observed, representing it in an outline of the animal's body, and 

 show in which segments the different ganglia occur. 



Exercise 16. Draw a diagram representing a side view of a grass- 

 hopper on a scale of 3 or 4, in which the segmentation, the relative 

 position of the heart, the alimentary tract, and the nervous system 

 are accurately indicated. 



