OF MYRIAPODA AN1) MACROUROUS ARACHNIDA. 
261 
to the Myriapoda, more especially to the latter, in the number of ganglia that enter 
into its composition. Thus there are six ganglia which belong to the head and 
thorax, and four of the seven that belong to the segments of the abdomen, which 
enter into the composition of the great nervous mass in the cephalothorax, while 
three remain in the abdomen and four in the caudal region, making seventeen sub- 
oesophageal ganglia, a number equal to that of some of the Myriapoda, and more 
than is ever found in any hexapod insect. 
The brain in the Scorpion (Plate XII. fig. 15. b) is exceedingly small. It is composed 
of two rounded, closely united ganglia, from the sides of which proceed directly 
upwards two small trunks, the optic nerves, which are given to the large median eyes 
(c) of the cephalothorax. At the base of these nerves, on the front of the brain, and 
arising from the same part, two other small trunks pass forwards and inwards to the 
middle line, around the muscles of the prehensile organs on the front of the head, and 
while passing outwards, on the upper surface, each is divided into separate branches 
for the lateral ocelli ( d ). These vary in number in different species. In Buthus, Leach, 
there are three on each side ; in Androctonus , Koch, there are five, but in Scorpius, 
Ehrenberg, only two. Immediately beneath the nerves to the eyes a large nervous 
trunk passes forwards, from the front of the brain on each side, to the small prehen- 
sile organs (a), which, in the Scorpions, are modified antennae. From the inner side 
of the front of each lobe of the brain, beneath these nerves to the antennae, a small re- 
current nerve passes forwards, and joins with its fellow on the opposite side to form 
a minute ganglion, from which a very small median trunk, the vagus*, passes back- 
wards beneath the brain for a short distance along the alimentary canal, but I have 
not yet been able to detect lateral ganglia connected with this trunk, as in the My- 
riapodes. The brain is connected with the medulla oblongata (e) by very short and 
thick crura, so that it scarcely appears distinct from the great nervous mass in the 
cephalothorax. The medulla oblongata ( e ) forms the first portion of this great mass, 
from which it is distinguished by a slight construction, although closely approxi- 
mated to it. It is spread out beneath the brain into a large concave ganglion, which 
gives off at its sides one very large pair of nerves, which are distributed to the great 
prehensile organs (1.), and which, from their origin, must be regarded as the ana- 
logues of the mandibles of insects, and of those of the forcipated foot jaws in the 
Chilopoda. These organs, as already shown by Savigny in other classes, are them- 
selves the analogues of those of locomotion, as is well exemplified in the anatomy of 
these organs in the Scorpions. The nervous mass behind this first ganglion gives off 
four pairs of large nerves (2. 3. 4. 5.) to the organs of locomotion, and four pairs of 
smaller ones (6. 7 - 8. 9.) to supply the abdominal segments, to which the trunks of 
these nerves pass backwards on each side of the cord, their ganglia being united 
with those of the thorax. The remaining ganglia of the abdomen (10. 11. 12.) are 
* This vagus nerve is very small, and has been omitted cn the drawing of the nervous system of the 
Scorpion, Plate XII., to avoid confusion. 
2 m 2 
