PHYSIOLOGY OF ASCIDIA ATRA LESUEUR 265 
addition, it brings about a discharge of the water present in the 
branchial sac. The stimulated siphon remains open, the other 
siphon closes tightly, and the animal contracts vigorously along 
its dorso-ventral axis, resulting in a sudden decrease in the ca- 
pacity of the respiratory chamber. Occasionally the stimulated 
siphon may also contract partially so as to decrease the size of 
its opening. This gives the ejected water a greater momentum. 
3) The last reaction of this group combines a bending of the 
body on its long axis with the movements of the previous response. 
This is the usual reaction which A. atra gives under ordinary 
conditions of stimulation of its internal surfaces. 
The last two reactions probably correspond to what Jordan 
(07) has described in Ciona as the ‘Ejektionsreflex’: ‘Closure 
of one siphon, rapid contraction of all muscles, other siphon 
(most frequently, but not always, the anal siphon) remaining 
open” (’07, p. 98). This description is repeated by Polimanti 
(11), who, however, added nothing to it. Jordan did not study 
this reflex at all, but contented himself with the statement that 
it serves to throw out foreign bodies, and that the causes for its 
appearance are not clear. 
In Ascidia there is no doubt about the nature of the aeaite 
which will produce any of these three crossed reactions. It is 
always a disturbance on the interior surfaces of the body. Ihave 
observed the same ‘Ejektionsreflex’ in the common Ecteinascidia 
turbinata of Bermuda under the same conditions of stimulation 
as in Ascidia atra. Jordan’s statement of its function is correct; 
it must, however, be broadened to include not only the ejection 
of foreign particles, but also the response to any internal irrita- 
tion, such as strong light or chemicals. 
The point of special significance is the crossed behavior of the 
siphon rims. Stimulation of the outside of a siphon causes that 
siphon rim to close. Stimulation of the inside of a siphon results 
in that siphon remaining open while the other siphon rim con- 
tracts. This points to the presence of a complexity of innervation 
in ascidians of which there has previously been no suspicion. 
The one factor which the six reactions of Ascidia possess in 
common is their negative character. A source of stimulation 
