142 M. straus-durckheim's 



strikingly, and observation confirms this. In Lucanus the 

 abdominal ganglia exist, but not in Melolontha. 



These laws, which we have pointed out as governing the 

 nervous system, are but the consequence of others more 

 general. These general laws shew us that the number and 

 size of the different nervous trunks depend always on the 

 functions of the organs to which they are distributed ; that 

 is to say, the largest are destined to the organs of the senses : 

 the next in size to the muscles, and the smallest to the vital 

 organs ; but the size of the nerves seems also to depend on 

 other causes, so that the first general rule we have pointed 

 out offers several exceptions. 



In the organs of the senses the size of the nerves appears to 

 be in an inverse ratio to the density of the agent to be per- 

 ceived : and as light is the most subtle of these, the eyes are, 

 cceteris paribus, the organs which receive the largest nerves. 

 Next in size are the antennal nerves, which may possess the 

 power of hearing ; then the nerves of the palpi. The man- 

 dibulary nerves, which, perhaps, enjoy the perception of taste, 

 are still smaller. The feet, as the organs of feeling, properly 

 so called, possess pretty considerable nerves ; lastly, the skin, 

 as the organ of the general sense of feeling, receives only very 

 small branches. 



In the second place, the size of the nerves is always in pro- 

 portion to the bulk of the organ to which they are directed, 

 and their thickness is also proportionate to the greater or less 

 complication of the organ, compared to its analogues in other 

 species. Lastly, the size of the nerve is always in relation to 

 the degree of sensibility of the organ in one species, as com- 

 pared with another. 



In the muscles, the nerves are, on one hand, proportioned 

 to their size, on the other to their activity. The vital organs, 

 which are not subject to the will, receive very small nerves in 

 proportion to their bulk. 



The trachece receive no nerves, but the respiratory muscles, 

 which are in part subject to the will, receive nerves less strong 

 than those of the organs of animal life, but more so than 

 those of vegetable life. 



The nervous trunks of the second size are distributed to 

 the vital organs ; those of the third size, to the secretory 

 organs. 



