PHYSIOLOGY OF ASCIDIA ATRA LESUEUR 267 
by Loeb (92). Although some of the results of Frohlich (03) 
on the removal of the ganglion of Ciona have been questioned by 
later authors (Jordan ’07, and Kinoshita 710), the combined 
work of all the investigators on Ciona proves that ganglion re- 
moval affects at least the threshold sensitivity, the tonus, and the 
rate of recovery after stimulation. 
Ascidia does not remain normal in the laboratory long enough 
to permit of a study of the quantitative effects of ganglion re- 
moval. I had, therefore, to content myself with a determination 
of the qualitative results produced by the mere nervous isolation 
of the two siphon regions from each other. This was accom- 
plished by means of a rapid incision into the test and mantle so 
directed as to result in the severing of the nervous mass into two 
parts. The animal recovered from this slight operation in a 
few minutes. 
The behavior of individuals under such nervous conditions was 
very instructive. Of the group of direct reactions, the first 
persisted, and seemed, qualitatively at least, to be normal. The 
second reaction, that is, the closure of both siphons, disappeared 
at once. As long as the whole animal was not jarred, no amount 
of contraction of one siphon called forth a similar response of the 
other siphon. The reaction involving the body flexure depends 
mainly on the bending of the oral siphon. Therefore when 
this siphon was stimulated the bending occurred, but the atrial 
siphon still remained unaffected. 
The essential element of the group of crossed responses is the 
closure of the siphon which is not stimulated. This element 
completely disappears after the operation. Stimulation of the 
inside of the oral siphon, frequently even when strong enough to 
involve the dorso-ventral contraction and the body bending, fails 
to affect the atrial siphon, and only causes a partial contraction 
of the oral one. Irritation of the inside of the atrial siphon 
brings about no change at all in the oral. 
These experiments leave no doubt of the ability of each portion 
of the animal to perform its part of a reaction even though it is 
isolated nervously from the rest. The reaction of the animal 
as a whole, however, depends on its nervous system being intact. 
