LESSON 72.] 



NERVOUS SYSTEM. 



239 



FIG. 



LESSON LXXIL 



NERVOUS SYSTEM OP CIREIPEDIA, AND MYRIOPODA. 



1086. In the Cirripedia (cirrus, a curl ; pes, a foot), commonly 

 called Barnacles, or Acorn-shells, the nervous system is very simple. 



1087. In the Lepas vitrea the oesophagus is surrounded by a 

 white oval ring, at the sides of which are placed the small ganglions 

 which supply the first pair of feet. The ring is completed below by 

 the ganglions of the second pair of feet. 



The fifth and sixth pairs of ganglions are 

 approximated to each other ; there is no 

 cerebral ganglion, but filaments are given 

 off from the supra-oasophageal loop to the 

 peduncle and sides of the head (see Fig. 

 363). Two of these branches pass to a 

 small ganglion on either side, near the 

 stomach, from which the digestive organs 

 are supplied; the tubular extensile tail 

 receives the last two pairs of nerves. The 

 neurolemma (nerve sheath) is stained by a 

 dark brown pigment in the Lepas vitrea. 



1088. The class Myriapoda (many 

 feet) contains the Wood-lice, lulidce (for 

 which there is no common name), and Cen- 

 tipedes (hundred legs). Both these latter 

 animals are found at the roots of trees ; 

 the lulus is about an inch in length (in 



this country), the body very round, covered by a brittle, black, shin- 

 ing skeleton ; its legs numerous, having two pairs on each segment 

 of the body, and remarkably short. Some species, if touched, throw 

 themselves on their side, and curl into a close ring. 



1089. In these animals the condition of the nervous system is of 

 much general interest. In them the corresponding ganglions of the 

 abdominal chords are much less conspicuous than in the earth-worms, 

 and the whole central axis of the nervous system, continued from the 

 brain, is almost as devoid of partial swellings as the spinal chord of 

 the apodal (without feet) vertebrates. 



1090. A figure of the brain and chief distribution of the nerves, 

 from an original preparation of lulus, is shown at Fig. 364. 



1091. The cephalic ganglion (a) of the lulus, is transversely 



Nervous system, Lepas vitrea 



(glassy). 



a, Nervous ring, surrounding 

 the oesophagus. 



5, c, Parallel nervous abdomi- 



nal chords. 



6, c, <?, e, f, Ganglia, supplying 



nerves to the curled feet. 



