1 8 THE INSECT WORLD. 



if one compares the oxygen they imbibe with the heavy organic matter 

 of which their body is composed, the amount is enormous. 



Before finishing this rapid examination of the body of an insect, 

 we shall have to say a few words on the nervous system. 



This system is chiefly composed of a double series of ganglions, 

 or collections of nerves, which are united together by longitudinal 

 cords. The number of these ganglions corresponds with that of the 

 segments. Sometimes they are at equal distances, and extend in a 

 chain from one end of the body to the other ; at others they are 

 many of them close together, so as to form a single mass. 



The cephalic ganglions are two in number ; they have been 

 described by anatomists under the name of brain. " This expres- 

 sion," says M. Lacordaire, " would be apt to mislead the reader, as 

 it would induce him to suppose the existence of a concentration of 

 faculties to control the feelings and excite the movements, which is 

 not the case."''' The same naturalist observes, "All the ganglions 

 of the ventral chain are endowed with nearly the same properties, 

 and represent each other uniformly." 



The ganglion situated above the oesophagus gives rise to the 

 optic nerves, which are the most considerable of all those of the 

 body, and to the nerves of the antennae. The ganglion beneath the 

 oesophagus provides the nerves of the mandibles, of the jaws, and of 

 the lower lip. The three pairs of ganglions which follow those placed 

 immediately below the oesophagus, belong to the three segments of 

 the thorax, and give rise to the nerves of the feet and wings. They 

 are in general more voluminous than the following pairs, which 

 occupy the abdomen. 



Fig. 15 represents the nervous system of the Carahiis atiratus : 

 A is the cephalic ganglion ; b, the sub-oesophagian ganglion ; c, the 

 prothoracic ganglion • d and e are the ganglions of the mesothorax 

 and metathorax. The remainder, f f, are the abdominal ganglions. 



Before finishing these preliminary observations, it is necessary 

 to say that the preceding remarks only apply absolutely to insects 

 arrived at the perfect state. It is important to m^ake this remark, 

 as insects, before amving at that state, pass through various other 

 stages. These stages are often so different from each other, that 

 it would be difiicult to imagine that they are only modifications 

 of the same animal ; one would suppose that they were as many 

 different kinds of animals, if there was not abundant proof of the 

 contrary. 



* " Introduction a rEntomologie," tome ii. p. 192. 8vo. Paris. 183S. 



