144 OUR HOUSEHOLD INSECTS 



consists of a chain of nervous centres or ganglia, in 

 pairs, connected with one another by nervous threads 

 (Fig. 43), and extending from one end of the body to 

 a the other. The greater part of it lies 



between the digestive tract and the 

 under surface of the body, and is 

 therefore nearest the ground when the 

 animal walks. Here again, therefore, 

 all preconceived notions gathered from 

 the familiar vertebrates are upset, as 

 we trace the great nerve-centres, not 

 down the back, but in exactly the 

 reverse position. The foremost pair 

 of ganglia, however, which are situated 

 in the head, and have been dignified 

 with the name of " brain," as they 

 send nerves to the sense organs, viz., 

 the eyes and antennas, lie above the 

 oesophagus, being connected by two 

 thick bands of nervous tissue with the 

 first pair that underlie it, so enclosing 

 that portion of the digestive tract as 

 in a collar. While examining the dis- 

 tended crop as it lies in its natural 

 FIG. 43. Nervous position, a small nervous ganglion may 



Chain of Cockroach, i u j TJ.J.I i. i i *.!_ i 



a, supra- cesopha- be observed as a little triangular whitish 

 ha; b, sub- ^ Q ^ Qn ^ upper surface about half-way 

 down its length. From this two nerves 

 minai ganglia. pags o bli que ly backwards towards the 

 hinder part of the crop, while a single one, running for- 

 ward along the middle line, connects this centre with 

 some small ganglia in the neighbourhood of the brain. 

 This small collection of nerves and ganglia is called the 

 visceral nervous system. 



