PHYSIOLOGY OF ASCIDIA ATRA LESUEUR 281 
2. Range of sensitivity 
The quantitative aspects of this sensitivity were rather baffling. 
The use of a tube in which warm or cold water circulated, as 
described by Kinoshita (10), was a complete failure because of 
the considerable mechanical stimulation accompanying its appli- 
cation to the tissues. Parker (’08) in his study of the sénsory 
reactions of Amphioxus found a similar method to be ineffective 
and for the same reason. 
The process of discharging seawater at different temperatures 
from a pipet also proved useless because of the extreme sensitiv- 
ity of Ascidia to the current which was set up. To avoid this, I 
attempted to fatigue an individual until it no longer responded 
to such a current of seawater at room temperature, and then 
discharged seawater at different temperatures near the oral si- 
phon. The results obtained in this way showed that the animals 
were thermosensitive. The method, however, proved too un- 
certain for quantitative measurements, tending to fatigue the 
experimenter as well as the animal. 
An attempt in still another direction was the following pro- 
cedure. An animal was fixed to the short arm of an L-shaped 
rod, the other arm of which was attached to a toy four-wheeled 
cart. This cart-moved on a smooth platform parallel to a trough 
in which the animal was submerged. The cart ran so smoothly 
that even so sensitive an animal as Ascidia remained open and 
expanded while it was moved the entire length of the 30-centi- 
meter trough. In this way Ascidia was converted from a sessile 
into a moving animal. <A temperature gradient was then ar- 
ranged in the trough and the animal moved into the different 
regions. This method, too, demonstrated the thermosensitivity 
of the species, because the animals gave an ejection reflex when 
brought into a region of higher temperature. It failed, however, 
to give satisfactory quantitative results. 
Finally I resorted to a modification of the pipet method by 
means of which its objectionable feature was eliminated. The 
tip of the pipet was covered with a layer of fine muslin, which 
was securely tied as near the tip as possible. The meshes of the 
