PHYSIOLOGY OF ASCIDIA ATRA LESUEUR 243 
the feces come out in neat, flat, oblong packets, they are incased 
in a thin layer of gelatinous material, which is probably the 
mucus. The presence of the gelatinous covering of the feces 
is best seen in animals which have been in the laboratory for 
some days. In such cases the feces contain but little excrement, 
and are composed mainly of a transparent mass of mucus. 
The seawater in the laboratory is coarsely filtered, and con- 
tains very few organisms. In this way the food supply of Ascidia 
is cut off; consequently, it, does not live long in confinement. 
This shows that the dissolved organic content of seawater, to 
which Pitter (07) has attributed such great importance, is of 
little significance in maintaining the metabolic balance of Ascidia. 
The species has developed an elaborate mechanism for capturing 
the organisms in seawater, and without them it slowly starves to 
death. 
IV. THE MOVEMENTS OF ASCIDIA 
Ascidia atra, though permanently attached to the rock, is 
capable of moving not only certain of its structures, but also of 
bending and contracting its body in relation to its base of attach- 
ment. The siphon rims can close and open, the body can con- 
tract along the dorso-ventral axis, and the entire animal can 
bend with a surprising degree of vigor. When arranged in 
certain combinations and sequence, these activities form the 
reflexes with which the animal responds to stimulation. From 
such an aspect they will be considered in the description of the 
sensory reactions of the species. At present, however, my object 
is to present the physiology of these movements in themselves 
by examining the factors which are concerned in their production. 
1. Siphon rim closure 
Ascidia is usually described as possessing eight lobes on the 
rim of the oral siphon and six on the atrial. These are shown in 
figure 1. All such photographs and desériptions are of dead 
animals and tell only a partial truth. In the normal, living 
animal under water, these lobes are not shrunken and collapsed, 
