THE NERVOUS SYSTEM. 81 



The nerves which are given off from the thoracic nerve centre, appear 

 to arise chiefly from its external or fibrous layer, hence it is difficult to 

 determine precisely to which ganglion they belong. Three large and two 

 small pairs arise from the upper, and an equal number from the under 

 surface of the nerve centre. 



The first large pair arise from the upper surface of the first pair of 

 ganglia ; they are distributed to the muscles of the pro-thorax, and pro- 

 bably also, to the integument.* A branch of this nerve ends in nerve 

 cells upon the thin lobes of the cephalo-sternum. 



The second pair arise with the last, and apparently supply the muscles 

 and integument of the pro-thorax. 



The third pair arise beneath the nerve centre, apparently between the 

 first and second ganglia, chiefly from the first ; they are especially dis- 

 tributed to the anterior pair of legs. They supply the muscles ; a large 

 terminal branch bifurcates in the tarsus, and supplies the integument of 

 the tarsup, the pulvilli and claws. 



The fourth pair are very large ; they arise from the upper surface 

 between the first and second ganglia. They chiefly supply the muscles of 

 the meso-thorax; they probably also supply the integument. A small 

 branch enters the subcostal nervure of the wing, and is distributed to 

 certain special structures described in Section XIII. 



The fifth pair arise from the under surface of the second pair of ganglia ; 

 they are distributed to the intermediate legs. Their distribution is similar 

 to that of the third pair. 



The sixth are a small pair from the upper surface of the second ganglia ; 

 they are probably chiefly nioior, and accessory to the fourth. 



The seventh pair are distributed to the halteres ; they arise from above 

 the junction of the second and third ganglia. 



The eighth are probably merely au oifaet of the ninth ; they are a small 

 pair like the second and sixth. I am not certain, whether these small 



* In, giving the distribution of these nerve*, 1 have attempted to give an 

 approximate idea; 1 ha/e only traced ike larger branches, and even that 

 LS a most minute and dinlcult dissection. Many which appear to end in 

 mutcles may pierce them, whence it is almost impossible to be quite certain 

 of their distribution. 



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