218 STUDIES IN GENERAL PHYSIOLOGY 



the regeneration of the central nervous system. Scarcely 

 another animal is so well adapted to the study of this prob- 

 lem as Ciona. The brain of Ciona consists of a snow-white 

 ganglion, somewhat larger than the head of a pin, situated 

 in the angle (/ near the surface between the two tubes a mid 

 b (Fig. 54 j. The mantle of Ciona is very transparent, so 

 that the ganglion can be removed with certainty with- 

 out seriously injuring the other organs of the animal. 

 The only difficulty encountered in the experiments is that 

 the animal contracts when touched, and that the ganglion 

 is then no longer visible. I overcame this difficulty in the 

 following way: The root of a Ciona which had been kept in 

 the aquarium was carefully detached from its base. The 

 animal was then quickly removed from the water and laid 

 upon a dark glass plate. As long as the animal was not 

 touched, it remained relaxed. I then brought the tip of a 

 pair of scissors behind the ganglion, and by a rapid cut sev- 

 ered the connection between the ganglion and the pedal part 

 of the body. Without removing the scissors, I seized the 

 ganglion with forceps, drew it out, and removed it by a 

 second snip of the scissors. 



The Ascidian usually bears the extirpation of the ganglion 

 well, and after the operation behaves in a way not expected 

 from our general conceptions of animal physiology. 



2. The first phenomenon worthy of note is that after 

 extirpation of the central nervous system the rcjle.rcs />rr- 

 sixt. Since Ciona is a sessile animal, the reactions of the 

 uninjured animal to external stimuli are limited to simple 

 contraction and stretching out of the body. This contraction 

 is brought about by a highly developed muscular system. 

 If the aquarium is slightly shaken, the animal contracts 

 quickly, to relax only when everything is again at rest. 

 Such a contraction of the whole animal also often follows 

 when it is carefully touched with the point of a needle. If 



