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tral diaphragm. This is a transparent, apparently structure- 

 less membrane, stretched over the floor of the abdominal 

 cavity in such a way as to protect the central part of the 

 nervous system. Owing to the transparency of this mem- 

 brane, it is very difficult to see it unless it is stained. The 

 ventral diaphragm is attached along each side of the body 

 just laterad of the great ventral muscles ; the points of at- 

 tachment are on the lines separating the segments of the 

 body. Between the points of attachment, the margins of 

 the membrane curve mesacl, giving it the appearance of be- 

 ing strongly stretched at the points of attachment. 



This diaphragm has been described as a ventral heart. 

 See Packard, Text Book of Entomology, p. 403. We believe its 

 function is to protect the central nervous system from the 

 peristaltic movements of the alimentary canal. 



The nervous system. After removing the alimentary 

 canal from the specimen opened along the back, the central 

 nervous system will be exposed. 



Make a diagram showing the disposition of the ganglia 

 and of the principal nerves of the thorax and abdomen. 

 These can be seen better in a specimen which has been 

 opened along the venter. Take for this purpose either a 

 fresh specimen or one that has been slit on the dorsal side, 

 and open it carefully on the ventral side so as to cut through 

 only the body-wall, leaving the nervous system in place. 



Make careful dissections of the ganglia and nerves found 

 in the head, and make a diagram showing their arrangement. 



The following parts should be observed and figured : 



The siipracesophageal ganglia. These are two, large, ovoid 

 ganglia, lying above the oesophagus, and connected by a 

 short, thick commissure. They are sometimes termed the 

 brain. 



The antennal nerves. These arise from the latero-cephalic 

 angles of the supracesophageal ganglia. 



