4?3 THE XER I'OUS S YSTEM. 



sists of two superimposed cords, an inferior cord with gang- 

 lionic enlargements, and a superior cord which is uninterrupted ; 

 and Newport found the same disposition in Insects and Arach- 

 nids. These statements have been amply confirmed, and such 

 strong evidence has been adduced in favour of the view that 

 the dorsal band of fibres in the ventral chain are conductors 

 between the cerebron and the ganglia of the ventral chain, 

 that this can scarcely be doubted ; Lemoine states that these 

 longitudinal fibres increase in number towards the brain, and 

 are four times more numerous between the first and second 

 thoracic, than they are between the last and penultimate 

 abdominal ganglia in the Crayfish (Astacus). They certainly 

 increase rapidly in number in the dorsal band of the thoracic 

 centre in the Blow-fly, from behind forwards. 



7. As the dorsal vessel continues to pulsate after the ablation 

 of the whole central nervous system, and after its removal 

 from the body (in Crustacea), it is probable that it has an in- 

 trinsic ganglionic mechanism ; it also receives accelerator 

 fibres from the stomogastric nerve (Lemoine) these may be 

 called the nerves of Lemoine and inhibitory fibres from the 

 thoracic ganglion (the nerves of Dogiel).Y ung confirms these 

 statements. Hence there is a complete analogy between the 

 nerve supply of the heart in Vertebrates and of the dorsal 

 vessel in Arthropods, lending additional evidence in favour of 

 the view that the thoracic ganglion corresponds to the medulla 

 oblongata, and the stomogastric with the sympathetic system 

 of the Vertebrate. 



Injury or ablation of the supra-resophageal centres has no 

 effect upon the pulsations of the dorsal vessel ; but stimulation 

 of the crura, from which the roots of the stomogastric nerves 

 arise, produces acceleration of the pulsations of the dorsal 

 vessel (Yung). 



