478 THE NERVOUS SYSTEM. 
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-cesophageal 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). 
