NERVOUS SYSTEM OF THE TUNICATE 313 



Not only did these amputated siphons exhibit independent 

 irritabiUty, but in the case of Ciona, an automatic rhythm was 

 also manifested by the severed oral siphons. A siphon which had 

 been cut off distal to the circlet of oral tentacles was observed 

 two days after the operation to execute a series of rhythmical 

 contractions which consisted of the periodic curling of the lip- 

 lobes either inward or outward and the occasional constriction 

 of the neck region. There was no special sequence in which the 

 several lobes took part in the contraction, for a contraction 

 would start on one side and be followed by a puckering, some- 

 times of the opposite side, sometimes of an adjacent part. The 

 proximal portion of the amputated piece, i.e., the region of the 

 cut margin, played no role in these contractions, the rhythmical 

 movements being restricted to the oral margin and to the di- 

 rectly underlying portion of the neck. In fact, when the proxi- 

 mal part was stimulated, the response occurred not in the 

 proximal end, but in the distal after a short latent period, the 

 impulse having traveled from the less irritable region of stimu- 

 lation to the more irritable region of the sensitive lobes before 

 producing a response. No attempt was made to analyze the 

 underlying phenomena of this response or to seek an explanation 

 of the rhythmicity. No such rhythm was observed for ampu- 

 tated siphons of Ascidia mentula. As it has frequently been 

 demonstrated that muscle tissue may be thrown into rhythmical 

 contractions by the presence of various salts in the water, this 

 rhythmical contraction in the Ciona siphon might have been due 

 to the automatic response of either the muscle or the nerve 

 tissue to the stimulating effect of the sea-water on the cut 

 surfaces. Whether sensory cells are present in the siphon 

 regions or not I have made no histological examination to 

 ascertain, but nerve fibers can be seen extending out into the 

 lip-lobes. 



Tunicates whose siphons had been amputated regenerated 

 new ones in the course of about three weeks, but amputated 

 pieces lived only five or six days and died without any sign of 

 beginning to regenerate a new body. 



THE JOURNAI, OF EXPEHIMENTAL ZOOLOGT, VOL. 28, NO. 2 



