220 STUDIES IN GENERAL PHYSIOLOGY 
were kept in the same vessel, and at the same distance 
below the surface of the water. Under a are given the 
height of the fall in normal, under 6 in brainless, animals. 
The figures are given only to show how constant is the differ- 
ence in the threshold of stimulation between the two ani- 
mals; the absolute height of the threshold of stimulation 
cannot be determined from them. 
a b 
8 mm. 65 mm. 
4 75 
10 80 
80 
In two other animals I obtained the following values. 
a b 
6 mm. 22 mm. 
8 20 
The temperature was 13° C. 
This difference in irritability may be due to the fact that 
the wave produced by the drop of water stimulates the motor 
nerves or muscles directly, and that the threshold of stimula- 
tion is higher for these than for the sensory nerve endings. 
3. It can be shown by a different experiment that another 
path for the conduction of stimuli must exist in the brain- 
less animal than in the uninjured, where stimuli no doubt 
travel over the nerves for the most part. If an incision is 
carefully made in the tube of a Ciona whose ganglion has 
been removed, not only the injured portion, but the entire 
animal, contracts, just as when the same stimulus is applied 
to an uninjured animal. This also may occur when one 
point of the oral edge is carefully touched with a needle. I 
imagine that in a brainless Ciona the motor nerves or muscles 
lying nearest the point of incision are stimulated mechani- 
cally, that these contract, and that the jarring or pulling 
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