84 Marvels of Pond-Life. 



ments of insects appear to be of this character, and 

 to be excited by the ganglia belonging to the 

 segment to which the moving limbs are attached. 

 Thus a centipede will run, after its head has been cut 

 off, and a water-beetle (Dytiscus) swam energetically 

 when thrown into water after its brain has been 

 removed."* 



It must not, however, be assumed that the brain of 

 insects has nothing to do with their movements. It is 

 probably the means of co-ordinating or directing them 

 to a common end, and gives rise to what are called 

 consensual movements, that is, movements which are 

 accompanied or stimulated by a sensation, although 

 not controlled by a will. In man these actions are 

 frequently exhibited, " as when laughter is provoked 

 by some ludicrous sight or sound, or by the remem- 

 brance of such at an unseasonable hour.^f Sneezing 

 is another instance of a sensation leading to certain 

 motions, without any intervention of the human will. 



Speaking of these consensual motions, Dr. Carpenter 

 observes, "It is probable, from the strong manifesta- 

 tions of emotion, exhibited by many of the lower 

 animals, that some of the actions which we assemble 

 under the general designation of instinctive are to be 

 referred to this group." 



The insect brain is composed of a supra-cesophagal 

 ganglion and infra- cesophagal one. Von Siebold says, 

 the first corresponds to the cerebrum of the vertebrata, 

 and " the second is comparable, perhaps, to the cere- 



* Carpenter's ' Manual of Physiology/ p. 551. 

 f Ibidi, p. 543. 



