262 SELIG HECHT 
Even here, however, the data are meager and scattered, and con- 
sist largely of incidental observations. This lack of knowledge 
and the abundant presence of Ascidia atra at Bermuda served 
as incentives for the following investigation of the sensory re- 
actions of this species. 
1. Description of reactions 
Jordan (’07) on the basis of his observations has called the 
ascidian Ciona, an animal poorinreflexes (reflexarmes Tier). With- 
out subscribing to any of his theoretical generalizations, which 
Baglioni (13) has justly criticized, I have no hesitation in simi- 
larly describing the behavior of Ascidia atra. Tests with a 
variety of conditions of stimulation have revealed very definite 
activities, by means of which the animals respond to changes 
in the environment. The number of these activities, however, 
is small. 
The structures and movements which are involved in their 
execution have already been described (Hecht, 717). It remains 
to explain their relation to one another and to the source of 
stimulation. The presence of the open siphons and of the water 
current makes it possible for Ascidia to receive indications of 
changes of the environment not only on its exterior, but also on 
its interior surfaces. This distinction is of fundamental im- 
portance, because the place of reception of the stimulus deter- 
mines the kind of movement which the animal executes. As a 
result there are manifested two qualitatively distinct groups of 
reactions. Each of the groups consists of three responses, which 
involve the use of different combinations of muscles. 
The group of direct responses depends for its origin on a source 
of stimulation which affects the external surface of the animal. 
This group of responses is concerned mainly with mechanical 
stimuli. Although the three reactions included under this head 
result from different intensities of the same outside disturbance, 
the reactions themselves involve an activity of different muscles, 
and not a different degree of activity of the same effectors. 
1) If the test of Ascidia be touched very lightly, the siphon 
nearer the point of stimulation will contract. The extent of the 
