320 EDWARD c. DAY 
vibratory stimulus, if sufficiently vigorous, will still induce 
closure of both siphons after the effects of shock have passed. 
Since both siphons respond without the ganglion and since 
the excurrent siphon which lacks the circlet of tentacles is about 
as sensitive as the incurrent siphon which has them, it would 
seem that neither circlet of tentacles nor ganglion is the re- 
ceptive organ for the vibrations, but that the lip-lobes them- 
selves are capable of responding to the Vibrations immediately. 
Hecht ('18) finds the lip-lobes to be the vibration receptors in 
Ascidia atra. 
SUMMARY OF REACTIONS OF ASCIDIA MENTULA 
A. Normal animal to tactile stimulation 
1. The margins of the siphons are the most sensitive part of 
the animal, and close when stimulated. 
2. To feeble stimulation the response is local and restricted to 
a single lobe of the siphon. To a stronger stimulus the whole 
siphon closes. Further increase of strength of the stimulus pro- 
duces a closure of the other siphon as well. 
3. There is a short latent period of about one-half second 
between the responses of the two siphons. 
4. The sequence of closure is reversible; the impulse travels in 
either direction from one siphon through the nerve ganglion to 
the other, depending upon which siphon is stimulated. 
5. Sometimes one siphon is more sensitiVe than the other and 
takes the initiative in the response when the two are stimulated 
simultaneously, as by Vibrations in the room. 
B. Operated animals to tactile stimulation 
a. With siphons amputated. 1. In a siphon partially slit longi- 
tudinally, each half responds locally to a feeble stimulus, While 
stronger stimulation sends the impulse around the cut and 
produces a response of the two halves in sequence. 
2. Amputated siphons retain their sensitivity for five or six 
days and then die. 
