292 SELIG HECHT 
TABLE 10 
ALKALOID CONCENTRATION 
Strychnine 0.00005 M 
Quinine 0.0004 M 
Morphine 0.001 M 
Anesthetics. Ether, chloral hydrated, ethyl aleohol and amyl 
aleohol all caused reactions which were very pronounced. The 
order of their effectiveness, taken from the values obtained in 
Exp. VIII.1.1 and VIII.2.2 and given in the accompanying table 
(table 11), is 
amyl ale. >chloral, ether >ethyl alc. 
TABLE 11 
ANESTHETIC CONCENTRATION 
Ether 0.02 M 
Chloral hydrated 0.02 M 
Ethyl aleohol 0.75 M 
Amyl alcohol 0.001 M 
6. Nature of the sense organs 
The morphological nature of the chemical, and indeed of any 
other kind of receptors in ascidians, is practically unknown. 
Seeliger (93-11, p. 323) has described, rather doubtfully and 
with much reserve, the presence of bristle cells on the tentacles 
of Ciona. Lorleberg (’07), however, failed to secure any trace 
of such structures in Styelopsis; although he found many regions 
richly supplied with nerve endings. It may then be that the 
organs of chemical sense in Ascidia are similar to those which 
underlie the common chemical sense of vertebrates (Parker, ’12). 
The physiology of the receptors would seem to favor such an 
assumption. The problem of the physiological nature of the 
chemical sense organs is simplified in Ascidia atra by the mo- 
notony of response to all classes of substances. This negative 
reaction of the crossed type and its variation with the intensity 
of the stimulus have already been made clear. We are, there- 
fore, dealing apparently with an automatic reflex, of which the 
receptor and effector mechanisms are all set, and the conduction 
