INSECTS IN GENERAL. 55 



and annelides. It consists in a nervous marrow, tolerably 

 homogeneous, most usually composed of twelve ganglia, 

 placed in lineal succession through the length of the body, 

 from the head to the opposite extremity of the trunk. From 

 these ganglia constantly proceed two nerves^ which go to 

 join the succeeding ganglion, and moreover other nerves, 

 variable in number, which proceed, radiating, to join the 

 surrounding organs, and whose thickness, or elongation, is 

 proportionate to the development of these organs, or their 

 distance from the ganglion. The principal ganglia are 

 generally thus disposed ; the first, which has been considered 

 as a brain, is situated in the head above the mouth and 

 the origin of the alimentary conduits. Besides the threads 

 which it furnishes to the different parts of the mouth, and 

 which it is not necessary to examine here, it sends some of 

 the thickest to the eyes and the antennfe, and two hindwards, 

 which connect the first ganglion to the succeeding. These 

 two threads constantly embrace the oesophagus, and thus 

 form a sort of collar, through which the aliments must pass. 

 The series of the other ganglia remains then under the intes- 

 tines and in the lower parts of the body. There are three in 

 the breast ; one for the prothorax, which gives out the nerves 

 of the fore feet ; one for the raesothorax, which furnishes the 

 nerves of the upper wings, or of the elytrae, and those of the 

 middle feet : finally, in the metathorax, the correspondent 

 ganglion, which is the fourth of the series, furnishes the 

 nerves of the lower wings and of the hinder feet. Kach of 

 them give out two threads, which establish the series of the 

 ganglia. In the abdomen, this series has as many ganglia 

 as there are rings, and these ganglia furnish the nerves of the 

 muscles, and those which accompany the tracheae, the geni- 

 tal, digestive, and secretory viscera. 



The larvae have the nerves differently arranged ; neverthe- 

 less, they are absolutely the same as those which shall be 



