192 NERVOUS SYSTEM. 



of the columns in the earth-worm, and one branch from each 

 side in the middle of the inter-ganglionic space. The sympa- 

 thetic and its ganglia are here extremely minute, as in the anne- 

 lides from the lengthened, straight, and narrow form of all the 

 nutritive organs. The second ganglion, or first sub-eesophageal 

 pair, has a very lengthened form, and its nerves proceed back- 

 wards at a very acute angle, to escape from the large and long 

 cephalic segment of the scolopendra. The nerves from the 

 ganglia I have observed more yellow and opaque than the trans- 

 parent and colourless filaments from the motor columns, as if 

 some of the cineritious globules of the ganglia were continued 

 into the sensitive portions of the mixed nerves. The great 

 toughness and density of the neurilema, which envelopes 

 the nerves of the myriapods and insects which breathe 

 atmospheric air, is seen by the stiffness with which the 

 most delicate and lengthened filaments project right out- 

 wards in a radiating manner from around all the ganglia ; the 

 nervous filaments are much softer in the Crustacea, mollusca, 

 and other aquatic animals, and the same difference is ob- 

 served in the density of their muscular fibres. From the 

 great size of the motor columns in the scolopendra, there is 

 a distinct lateral longitudinal groove of separation between 

 them and the inferior or sensitive chords, and on seizing the 

 fourth or last pair of nerves from each ganglionic space, and 

 raising them upwards, the large motor columns I have found 

 to be nearly as easily separable from the sensitive beneath 

 them, as those which I have demonstrated, for many years 

 past, as the motor columns of the scorpion (Fig. 84. B. a, G,) 

 and which have more recently been imagined to be res- 

 piratory nerves in the muscular tail of that pulmonated 

 animal. 



The abdominal nervous columns of insects have been cor- 

 rectly regarded by Lyonet, Straus, Dufour, Chiaje, and most 

 others, as analogous to the spino-cerebral axis of vertebrata, 

 and the first of these writers has described them seventy years 

 ago, as similar in anatomical structure and physiological proper- 

 ties to the spinal chord of the highest animals. There are gene- 

 rally at first thirteen pairs of approximated ganglia correspond- 

 ing with the original segments,and extended along the middle 

 of the ventral surface of the body, as shown by Lyonet in the 

 caterpillar of the cossus, and the oesophagus pas'ses downwards 



