THE ANATOMY OF INSECTS. 35 



In addition to the central nervous system described above, there 

 is what has been termed the visceral nervous system. This consists 

 of two parts, the (KSOpkageal nerves, and the respiratory nerves. 



There are two sets of cesophageal nerves, the unpaired and the 

 paired. From each of the nerve-cords that connect the brain with 

 the suboesophageal ganglion there arises a nerve, which extends 

 cephalad upon the oesophagus; these unite to form the frontal 



Jion (Fig. 44, c)* From this ganglion a recurrent nerve passes 

 caudad through the oesophageal collar between the aorta and the 

 oesophagus. A short distance caudad of the brain, this nerve, in 

 some insects, enters a small ganglion, from which branches extend 

 to the sides of the alimentary canal ; in other insects it forms a 

 number of plexuses in the muscular layer of that organ without 

 apparent ganglia. These ganglia and nerves comprise the unpaired 

 m. The paired oesophageal nerves arise on either side from 

 the caudal aspect of the brain, and swell out at the sides of the 

 oesophagus to form ganglia (Fig. 44, d} which also supply nerves 

 to the walls of the alimentary canal. 



The respiratory nerves are not represented in the figure of C 

 dalus ; but they are well shown in that of the larva of Cossus (Plate 

 I.). They consist of the following parts: In each segment of the 

 thorax and abdomen there is a short longitudinal cord between the 

 cords of the central nervous system. Each of these cords en- 

 larges into a ganglion, from which branches extend laterally to the 

 sides of the body, where they supply the tracheal trunks and the 

 muscles of the spiracles. 



Organs of Special Sense. It is probable that insects po- 

 the five senses known to us; and perhaps they have others tin 

 tu re of which we cannot conceive. Even in the case <>f the five 

 senses, the range of perception may be very different from ours. 

 Thus Lubbock has shown that ants perceive the ultra-violet rays, 1 

 which are invisible to us. Tin-re is, however, a great variation in 

 the degree of development of the different senses in different in- 

 r example-, some are furnished with wonderful eyes, while 

 PC blind. It is pr. >l>abl" that in man; 

 opment of one sense i^ correlate <1 with a >li-ht development of KM 



:il the I 



cadas, which ;idi- 



* Sec /r ' i the Nervous Sysicn 



rydalus cornutus : an extract from a thesis in <y present 



Cornell Univer^ Baccalaureate in Science : . 1 84. 



