36 COMPARATIVE PHYSIOLOGY OF THE BRAIN 



that it becomes small and round. This reflex is de- 

 termined by two groups of muscles, first by ring- 

 muscles in the oral and aboral openings, second by 



longitudinal muscles, 

 which run lengthwise 

 through the animal. By 

 the contraction of these 

 muscles the animal is 

 protected from the en- 

 trance of foreign bodies 

 into the body cavity. 

 This reaction is a typ- 

 ical reflex act, and is 

 eminently purposeful. 

 According to the pre- 

 vailing ideas concern- 

 ing the decisive role 

 that the ganglion plays 

 in reflexes, the pro- 

 cedure is as follows : 



If the oral or aboral 

 opening be touched, the stimulation is conducted 

 through the peripheral nerves to the ganglion, where 

 a mysterious reflex mechanism is brought into play, 

 which gives the muscles the command to contract in 

 a manner corresponding to the nature of the stimulus. 

 Ferrier, for instance, in his text-book, mentions the 

 one ganglion of the Ascidians as illustrative of the 

 significance of the ganglion in reflexes. 



I removed the ganglion from a number of Cionse. 



FIG. 9. CIONA INTESTINALIS. 



a oral, b aboral opening ; c, foot, d, location of 

 ganglion. 



