Norman, Nervous System of Arthropods. 235 



the animal resting quietly suddenly begins the walking-move- 

 ments without changing position, then stops these and begins 

 to rub itself, etc. 



The assertion that the brain of Arthropods is an inhibitory 

 organ is supported by the following facts : 



1. It was observed in almost all of the animals experi- 

 mented upon, that reflex actions of an animal deprived of its 

 brain are called forth by such stimuli as under normal conditions 

 fail to cause a reaction. 



2. The animals operated upon are in almost continual 

 motion and rarely make a pause, while the same animals under 

 normal conditions often remain quiet for a long time and ex- 

 ecute movements only when there is cause. Astacus and Car- 

 cinus work the mouth organs almost unceasingly even when 

 they have no food ; also even without the application of any 

 stimulus. Carcini, Astaci, Squillae, Apes and Dystici deprived 

 of their brain, rub themselves by the hour, or make, even when 

 lying on their backs, powerless walking movements. The only 

 animal in which this was not clearly the case was the grass- 

 hopper (Pachytylus). Through lack of inhibitory impulses 

 the motions of the animals are purposeless. The inhibition 

 arising from each half of the brain extends only to the corres- 

 ponding side of the body, since only upon that side of the body 

 on which the oesophageal commissure is cut, or the half of the 

 brain is removed appear the continued actions of the extremi- 

 ties. This increase in motion upon the operated side is very 

 plainly present in all of the animals upon which I operated, in- 

 deed even in Pachytylus it is decidedly expressed, where extir- 

 pation of the whole brain gave no definite result. The strong- 

 est proof for the inhibition theory is the circular motion to the 

 side of the uninjured half of the brain, which appears always 

 in the case of some animals (Pachytylus, Apus), frequently in 

 the case of others (Astacus, Squilla, Dytiscus), after removal 

 of one half of the brain, and which I believe must be referred 

 solely to the freedom from inhibition on the operated side of 

 the body. 



