296 SELIG HECHT 
One such attempt has been made. On the basis of his work 
on echinoderm eggs and Arenicola larvae, Lillie (11) has proposed 
an explanation for general irritability. It is, that sensory stimula- 
tion means an increase in the permeability of the irritable element. 
Lillie’s explanation is based on the assumption that the de- 
marcation current and kindred phenomena are functions of the 
differential permeability of the cell membrane to certain sub- 
stances, notably H and OH ions. The work of Loeb and Beutner 
(14) has, however, shown that this bioelectric potential is due 
on the contrary to the presence of certain lipoid materials in the 
protoplasm. It is still uncertain to what extent differential 
solubility and the effect of interphase boundaries are concerned 
in the interpretation of these results. It is much to be regretted 
that the experiments were discontinued. 
There is, moreover, another and more significant objection to 
Lillie’s idea. All the substances which increase permeability 
undoubtedly do stimulate. But many substances, like Ca and 
the anesthetics in general, all of which have a decreasing action 
on permeability (Osterhout, ’16), also serve as vigorous stimu- 
lants to Ascidia and other aquatic organisms. 
The theory in its present form can therefore not be accepted 
as an adequate explanation. However, the attempt at an inter- 
pretation along the lines of permeability and similar concepts 
is entirely in the right direction. 
VI. SUMMARY 
+ 
1. Ascidia possesses six distinct reactions to stimuli, all of 
them negative in character. They may be divided into two 
groups of three each: the direct reflexes, which depend upon a 
stimulation of the exterior of the body, and the crossed reflexes, 
which depend upon a stimulation of the interior of the body. 
2. Theintersiphonal ganglion connects the two siphons. Sev- 
ering this nervous mass completely abolishes the crossed reactions, 
and interferes with the direct ones. Nevertheless, each portion 
of the animal is able to perform its part of a reaction, even though 
nervously isolated from the rest. 
