Packard.] MENTAL POWERS OP INSECTS. 359 



this chain of ganglia is really a series of brains, so that if 

 insects think at all the process is carried on in the abdomen 

 as well as the trunk or the head ! 



This accounts for the fact that when insects are deprived 

 of their head, or abdomen, they will sometimes continue to 

 live for man}' hours. They still have a few pairs of brains 

 left. 80 also when the sand wasp stings the caterpillar or 

 spider in the thorax its whole body is paralyzed. Probably 

 the brain proper is never injured, as the sting is not known 

 to penetrate the head. 



The hairs of insects found scattered over the body, par- 

 ticularly those on the feelers and the more exposed parts of 

 the bod}-, are often provided with a nerve, and are exceed- 

 ingly delicate tactile organs. Mr. R. Beck "suggests that 

 spiders are capable of distinguishing sounds to some extent 

 by means of very delicate waving hairs, which are found on 

 the upper surfaces of their legs. During life they move at 

 their peculiarly cup-shaped bases, with the least motion of 

 the atmosphere, but are immovable after death. It is well 

 known that sound is due to vibrations which are generally 

 conveyed by undulations of the air ; now I am perfectly 

 satisfied that if these undulations are of a certain character 

 the hairs I am alluding to, upon the spider's leg, will move, 

 and I wish you particularl}' to notice that they are of differ- 

 ent lengths, so that some might move whilst others would 

 not, and also that the longest is at the extremity of the leg, 

 and therefore can receive an undulation which miglit die 

 away higher up. I may thus mention that there is a group 

 of these peculiar hairs on the flea. The legs of a si)ider are 

 most sensitive organs of feeling, if they do not also embrace 

 those of hearing." The reader is by this statement reminded 

 of the interesting discovery of Dr. Johnson, confirmed and 

 extended by Professor A. M. Mayer, regarding the sense of 

 hearing in the mosquito, which we have already referred to 

 in a previous chapter. 



