Central Nervous System of a Centiped 



ARTHUR S. CAMPBELL 



The central nervous system of S. Polymnrfi/in Woods, is especially studied in the 

 present paper. 



Hymonds (1898) considers the development giving especial note to the homologies 

 of this system. Newport (1843) gives some notes in regard to the brain. Saint-Remy 

 (1890) gives considerable detail especially in regard to the finer structure of the 

 brain of S. Morsitans L. Case (1920) has shown something of the behavior of 

 S. Polymop/ia and indirectly the arrangement of never tracts. 



Ordinary dissections and the occaasional use of a binocular microscope proved 

 the most useful. 



Successful stains were Heidenheim's and Delafield's Haemetoxlins. HgCl.- or 

 AgN'Oa seemed the best fixers. Tracheae were studied without reagents immediately 

 after exposure. 



In S. Polymorpha the supraoesophagal ganglion or brain comprises three paired, 

 fused divisions or lobes. Large branches extend from the antenna] lobes into the 

 antennae. The ocular lobe fuses with this and is distinctly larger and less markedly 

 hilohate. This lobe sends out nerves to the oceili. The labro-fontal division is under- 

 neath the ocular lobe and entirely fused with it. It innervates the labrum. 



The supraoesophageal ganglion in S. Polymorpha is large. It is anteriorally 

 connected with the brain by two circumoral connectives. Ten principal, paried 

 nerves are connected with this ganglion. The anterior pair extend into the mandibles. 

 The second pair supplies the first maxillae, the third runs to the second maxillae. The 

 fourth pair innervates the maxillipeds. The fifth pair supplies the prehensorial 

 feet. 



The remaining somites are supplied by simple, similar ganglia, equally spaced 

 but well separated by connectives. The third and fourth ganglia area almost fused, 

 due to the foreshortened segments in which they are located. There is no histological 

 difference between them and other abdominal ganglia. One ganglion only is present 

 in each somite. Altogether in S. Polymorpha there are twenty-four ganglia. 



Each abdominal ganglion gives off eight nerves. There is no ventral nerve. The 

 first pair of branches supplies the tergular muscles, the second the walking legs, the 

 third the sternal muscles and the fourth supplies the spiracles and tracheae. 



The two caudal ganglia present special interest. Four principal branches run 

 from the first of these. The first supplies the tergal muscles, the second the sternal 

 muscles while the fourth supplies the anal legs. Additionally, two preanal connectives 

 join with a small ganglia about half the normal size of the others. Four nerves 

 extend from this last small ganglion into the sphincter and other anal muscles. 



In general the superficial tracheal distribution is rather definite and much 

 resembles that of the insects. The brain is rather poorly supplied by but two main 

 tracheae on either side which break up into a number of tracheoles which run into 

 the antennae and optic lobes. In contrast to this, the suboesophageal ganglion is 

 supplied dorsally by three tracheaae on each side. 



