LESSON 72.] NERVOUS SYSTEM, 241 



illse, which form the under lip ; the nerves of the two single pairs of 

 feet, belonging to the thoracic segments, next arise, and afterwards 

 the more numerous minute nerves to the little feet, which, by their 

 articulation to the segments in double pairs, indicate pw} gg5 

 such segments to be merely a confluence of two seg- 

 ments. The simplicity of the abdominal chords cor- 

 responds with the close approximation and great num- 

 bers of the organs from which they receive impres- 

 sions, and to which they transmit stimuli. 



1095. In the Polydesmus maculatus (spatted), 

 (Fig. 365), the segments are fewer and larger than in 

 the lulus, and their lateral margins are produced; 

 each, however, with the exception of the first three, 

 which answer to the thorax in insects, supports two 

 pairs of legs but these are longer than in the lulus. 



1096. The abdominal nervous chords show as lit- 

 tle trace of their median separation as in the luli, 

 swelling into two slight enlargements (a, a) opposite 2JA 

 each of the abdominal segments ; two nerves are sent 



off from either side of each enlargement, and the an- BJ1 



terior of these four pairs of nerves is directed at an 



acute angle forwards and outwards to the stigmata; 



it is doubtful, however, if these be nerves analogy 



seems to indicate that they are arteries ; the remaining pairs supply 



the muscles of the segment, and the legs, and are of equal size. 



1097. In the Centipede (Scolopendra), a series of equal and equi- 

 distant ganglia is developed upon the" ventral surface of the two ab- 

 dominal chords. Only in the first and last of the abdominal gangli- 

 ons can any modification of size be detected. The anterior or 

 sub-cesophageal ganglion is larger than the rest, having to supply 

 the modified legs which perform the function of jaws and underlip ; 

 the chords diverging as they escape on each side of the oesophagus, 

 enclose it by uniting with the large bilobed brain above. The nerves 

 from this part (the brain) supply the large antennae and the aggre- 

 gated ocelli ; in other words, the organs of special sense. 



1098. Even in animals so low in the scale of being as the class 

 Myriapoda, we find the full recognition of the leading physiological 

 divisions of a nervous system in the higher animals. 



1099. Thus the supra-cesophageal ganglion or brain in these crea- 

 tures, so far corresponds with the cerebrum of Man, that it is sub- 

 servient to the functions of the special organs of sense, and is the 



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