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 d near the surface between the two tubes @ and 
b (Fig. 54). 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 sey- 
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 reflexes per- 
sist. 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 
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