n6 COMPARATIVE PHYSIOLOGY OF THE BRAIN 



on the central nervous system of these animals have 

 unquestionably been made by Bethe, and we shall in 

 the main follow his presentation. Many of the facts 

 which Bethe describes from the animals used in his 

 experiments are familiar to me from personal observ- 

 ation, and I am convinced that the picture he gives 

 is correct. 



If in a crayfish both the commissures (c, Fig. 32) 

 which connect the supracesophageal ganglion o with 

 the rest of the brain be severed, the behaviour of the 

 animal is no longer controlled by the brain o. It does 

 not make spontaneous progressive movements. When 

 stimulated it begins to move, but after having gone 

 about 20 cm. it stops. This lack of spontaneous pro- 

 gressive movements agrees with the description given 

 by Flourens of the Vertebrate from which the cere- 

 bral hemispheres had been removed. Flourens's repre- 

 sentation was wrong, however, for a dog operated 

 upon in this way shows increased spontaneity in its 

 progressive movements. 



Annelids and Arthropods are closely related as re- 

 gards the central nervous system. However, Nereis 

 shows an excess of progressive movements after 

 removal of the supracesophageal ganglion, while As- 

 tacus no longer moves spontaneously. I believe that 

 the difference depends only upon circumstances of 

 minor importance. Ward has already found and 

 Bethe has confirmed the fact that in brainless cray- 

 fish the legs are unceasingly active, either cleaning 

 each other or performing pendulum -movements. 



