40 



dense connective tissue ; it takes a bluish colouration in 

 preparations treated with. Mann's methyl-blue-eosin. 



Lying immediately dorsad of the ventral nerve chain 

 there exists what ma}' be regarded as a median accessory 

 nerve cord [in.n. in figs. 46 and 48). It is confined to the 

 region of the thorax, and is present between and above 

 each pair of connectives joining the thoracic ganglia. It 

 does not appear as a continuous cord, but is seen to arise 

 from the sub-cesophageal ganglion, and from there to pass 

 backwards to the anterior border of the prothoracic 

 ganglion, where it appears to terminate. It then, 

 however, takes fresh origin from the hinder margin of 

 the latter ganglion, and is continued backwards to the 

 mesothoracic ganglion. After repeating itself again, it 

 finally terminates in the ganglion in the metathorax. 

 This system is very delicate, and is difficult to make out ; 

 it is probable that its fibres pass as a continuous strand 

 through each of the ganglia, and so connect together each 

 section of the cord. Three pairs of transverse nerves 

 belong to this accessory nerve cord [m.n. hr. in fig. 48), 

 and in one or two fortunate preparations they were seen 

 to pass to certain j^arts of the ventral muscvdature. 



A similar accessory system to the above has been 



described by Oudemans in the Thysanuran Machilis. It 



is there found in relation with each pair of ventral 



ganglia throughout the whole length of the body, and is 



said to supply the tracheal trunks and the occlusor 



muscles of the spiracles. There appear to be no grounds 



for regarding this system, either in Anurida or Machilis 



as being of a sympathetic nature.' In Anniida its 



* In the CoUembola a "true sympathetic (stomatogastric) system 

 has been described and figured by Willem in Podura aquatica. It is, 

 however, only very feebly developed. No certain indications of such a 

 system have been met with in Anurida. Claypole states that in the 

 embryo of the latter a cord -like proliferation of ectoderm cells arises 

 from the hinder end of the stoniatodoeum, and regards it as a remnant 

 of a sympathetic system ; it disappears, however, before hatching. 



